Gill Sans Bold

Engineering Studies
HSC Course
Stage 6

Telecommunications engineering

ES/S6 HSC 41098 P0022162

Acknowledgments
This publication is copyright Learning Materials Production, Open Training and Education Network
Distance Education, NSW Department of Education and Training, however it may contain material from
other sources which is not owned by Learning Materials Production. Learning Materials Production
would like to acknowledge the following people and organisations whose material has been used.
Board of Studies, NSW

All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in
good faith.

Materials devlopment: Paul Soares, Harry Taylor, Ian Webster

Coordination: Jeff Appleby
Edit: John Cook, Josephine Wilms, Stephen Russell, Steve Cavanagh (BOS)
electricity/electronics component
Illustrations: Tom Brown, Barbara Buining
DTP: Nick Loutkovsky, Carolina Barbieri

Copyright in this material is reserved to the Crown in the right of the State of New South Wales.
Reproduction or transmittal in whole, or in part, other than in accordance with provisions of the
Copyright Act, is prohibited without the written authority of Learning Materials Production.

Learning Materials Production, Open Training and Education Network Distance Education,
NSW Department of Education and Training, 2000. 51 Wentworth Rd. Strathfield NSW 2135.

Revised 2002
Module contents

Subject overview .......................................................................................... iii

Module overview .........................................................................................vii

Module components .................................................................................... vii

Module outcomes ......................................................................................... ix

Indicative time ...............................................................................................x

Resource requirements................................................................................. xi

Icons ...................................................................................................xiii

Glossary ................................................................................................... xv

Directive terms..........................................................................................xxiii

Part 1: Telecommunications engineering

scope of the profession & engineering report................ 145

Part 2: Telecommunications engineering

history of telecommunications.......................................... 145

Part 3: Telecommunications engineering

materials .............................................................................. 137

Part 4: Telecommunications engineering

mechanics and hydraulics ................................................ 133

Part 5: Telecommunications engineering

electricity/electronics ......................................................... 165

Part 6: Telecommunications engineering

communications ................................................................. 144

i
 Bibliography.................................................................................................39

Module evaluation ......................................................................................43

ii
Subject overview

Engineering Studies Preliminary Course

Household appliances examines common appliances
found in the home. Simple appliances are analysed
to identify materials and their applications.
Electrical principles, researching methods and
techniques to communicate technical information are
introduced. The first student engineering report is
completed undertaking an investigation of materials
used in a household appliance.

Landscape products investigates engineering

principles by focusing on common products, such as
lawnmowers and clothes hoists. The historical
development of these types of products demonstrates
the effect materials development and technological
advancements have on the design of products.
Engineering techniques of force analysis are
described. Orthogonal drawing methods are
explained. An engineering report is completed that
analyses lawnmower components.

Braking systems uses braking components and

systems to describe engineering principles. The
historical changes in materials and design are
investigated. The relationship between internal
structure of iron and steel and the resulting
engineering properties of those materials is detailed.
Hydraulic principles are described and examples
provided in braking systems. Orthogonal drawing
techniques are further developed. An engineering
report is completed that requires an analysis of a
braking system component.

iii
 Bio-engineering both engineering principles and also
the scope of the bio-engineering profession. Careers
and current issues in this field are explored.
Engineers as managers and ethical issues confronted
by the bio engineer are considered. An engineering
report is completed that investigates a current bio-
engineered product and describes the related issues
that the bio-engineer would need to consider before,
during and after this product development.

Irrigation systems is the elective topic for the

preliminary modules. The historical development of
irrigation systems is described and the impact of
these systems on society discussed. Hydraulic
analysis of irrigation systems is explained. The
effect on irrigation product range that has occurred
with the introduction of is detailed. An engineering
report on an irrigation system is completed.

iv
HSC Engineering Studies modules
Civil structures examines engineering principles as
they relate to civil structures, such as bridges and
buildings. The historical influences of engineering,
the impact of engineering innovation, and
environmental implications are discussed with
reference to bridges. Mechanical analysis of bridges
is used to introduce concepts of truss analysis and
stress/strain. Material properties and application are
explained with reference to a variety of civil
structures. Technical communication skills
described in this module include assembly drawing.
The engineering report requires a comparison of two
engineering solutions to solve the same engineering
situation.

Personal and public transport uses bicycles, motor

vehicles and trains as examples to explain
engineering concepts. The historical development of
cars is used to demonstrate the developing material
list available for the engineer. The impact on
society of these developments is discussed. The
mechanical analysis of mechanisms involves the
effect of friction. Energy and power relationships are
explained. Methods of testing materials, and
modifying material properties are examined. A
series of industrial manufacturing processes is
described. Electrical concepts, such as power
distribution, are detailed are introduced. The use of
freehand technical sketches.

Lifting devices investigates the social impact that

devices raging from complex cranes to simple car
jacks, have had on our society. The mechanical
concepts are explained, including the hydraulic
concepts often used in lifting apparatus. The
industrial processes used to form metals and the
methods used to control physical properties are
explained. Electrical requirements for many devices
are detailed. The technical rules for sectioned
orthogonal drawings are demonstrated. The
engineering report is based on a comparison of two
lifting devices.

v
 Aeronautical engineering explores the scope of the
aeronautical engineering profession. Career
opportunities are considered, as well as ethical
issues related to the profession. Technologies
unique to this engineering field are described.
Mechanical analysis includes aeronautical flight
principles and fluid mechanics. Materials and
material processes concentrate on their application
to aeronautics. The corrosion process is explained
and preventative techniques listed. Communicating
technical information using both freehand and
computer-aided drawing is required. The
engineering report is based on the aeronautical
profession, current projects and issues.

Telecommunications engineering examines the

history and impact on society of this field. Ethical
issues and current technologies are described.
The materials section concentrates on specialised
testing, copper and its alloys, semiconductors and
fibre optics. Electronic systems such as analogue
and digital are explained and an overview of a
variety of other technologies in this field is
presented. Analysis, related to telecommunication
products, is used to reinforce mechanical concepts.
Communicating technical information using both
freehand and computer-aided drawing is required.
The engineering report is based on the
telecommunication profession, current projects and
issues.
Figure 0.1 Modules

vi
Module overview

Telecommunications engineering is the final focus module in the HSC

course. This field of engineering, its history and impact on society are
discussed. Ethical issues and current technologies are described. The
materials section concentrates on specialised testing, copper and its
alloys, semiconductors and fibre optics. Electronic systems such as
analogue and digital are explained and an overview of a variety of other
technologies in this field are described. Analysis, related to
telecommunication products, is used to reinforce mechanical concepts.
Communicating technical information using both freehand and computer
aided drawing is required. The engineering report is based on the
telecommunication profession, current projects and issues.

Module components
Each module contains three components, the preliminary pages, the
teaching/learning section and additional resources.
The preliminary pages include:
module contents
subject overview
module overview
icons
glossary
directive terms.

Figure 0.2 Preliminary pages

vii
 The teaching/learning parts may
include:
part contents
introduction
teaching/learning text and tasks
exercises
check list.

Figure 0.3 Teaching/learning section

The additional information may

include: Additional
resources

module appendix
bibliography
module evaluation.

Figure 0.4 Additional materials

Support materials such as audiotapes, video cassettes and computer disks

will sometimes accompany a module.

viii
Module outcomes
At the end of this module, you should be working towards being able to:
describe the scope of engineering and critically analyse current
innovations (H1.1)
differentiate between properties of materials and justify the selection
of materials, components and processes in engineering (H1.2)
analyse and synthesise engineering applications in specific fields and
report on the importance of these to society (H2.2)
use appropriate written, oral and presentation skills in the preparation
of detailed engineering reports (H3.2)
investigate the extent of technological change in engineering (H4.1)
appreciate social, environmental and cultural implications of
technological change in engineering and apply them to the analysis of
specific problems (H4.3)
select and use appropriate management and planning skills related to
engineering (H5.2)
demonstrate skills in analysis, synthesis and experimentation related
to engineering (H6.2).

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

ix
 Indicative time
The Preliminary course is 120 hours (indicative time) and the HSC course
is 120 hours (indicative time).

The following table shows the approximate amount of time you should
spend on this module.

Preliminary modules Percentage of time Approximate

number of hours

Household appliances 20% 24 hr

Landscape products 20% 24 hr

Braking systems 20% 24 hr

Bio-engineering 20% 24 hr

Elective: Irrigation systems 20% 24 hr

HSC modules Percentage of time Approximate

number of hours

Civil structures 20% 24 hr

Personal and public transport 20% 24 hr

Lifting devices 20% 24 hr

Aeronautical engineering 20% 24 hr

Telecommunications engineering 20% 24 hr

There are six parts in Telecommunications engineering. Each part will

require about four hours of work. You should aim to complete the
module within 20 to 25 hours.

x
Resource requirements
During this module you will need to access a range of resources
including:
Part 3 Experiment
Multimeter
Test items coffee mug, telephone body, metal knife, etc.
OR
Small dry cell battery
2 elastic bands
3 pieces of wire or two paper clips
Torch globe
Test items coffee mug, telephone body, metal knife, etc.
Part 3 Activities
Old telephone
OR
Your current telephone
Part 3 Exercise
small dry cell battery
two elastic bands
3 pieces of wire or 3 paper clips
torch globe
Part 6 Exercise
tape measure
paper
sharp pencils.

xi
xii
Icons

As you work through this module you will see symbols known as icons.

The purpose of these icons is to gain your attention and to indicate

particular types of tasks you need to complete in this module.

The list below shows the icons and outlines the types of tasks for Stage 6
Engineering studies.

Computer
This icon indicates tasks such as researching using an
electronic database or calculating using a spreadsheet.

Danger
This icon indicates tasks which may present a danger and
to proceed with care.

Discuss
This icon indicates tasks such as discussing a point or
debating an issue.

Examine
This icon indicates tasks such as reading an article or
watching a video.

Hands on
This icon indicates tasks such as collecting data or
conducting experiments.

Respond
This icon indicates the need to write a response or draw
an object.

Think
This icon indicates tasks such as reflecting on your
experience or picturing yourself in a situation.

xiii
 Return
This icon indicates exercises for you to return to your
teacher when you have completed the part. (OTEN OLP
students will need to refer to their Learner's Guide for
instructions on which exercises to return).

xiv
Glossary

As you work through the module you will encounter a range of terms that
have specific meanings. The first time a term occurs in the text it will
appear in bold.

The list below explains the terms you will encounter in this module.
alternating current current that varies with time
ampere (A) the unit for current flow in a conductor
amplification an increase in the energy of a signal
amplitude modulation a modulation scheme in which the information to
be transmitted is contained in the instantaneous
variations in the amplitude of a modulated carrier
wave
amplitude shift keying an amplitude modulation scheme in which the
message signal is a digital signal
analogue signal a signal that is continuous in both amplitude and time
analogue transmission the use of a continuously varying signal to send
information
ASCII code a coding scheme that uses a specific set of binary
characters to represent alphanumeric and control
characters for computing and telecommunications
attenuation a decrease in the intensity of light travelling in a
fibre; can also refer to other forms of energy, for
example electrical signals and radio waves
bandwidth the range of frequencies available in a particular
band; the range of frequencies that can propagated
by a channel; the range of frequencies that make up
a signal
baseband the frequencies at which a signal is generated
battery electrical component used to create and store an
electrical charge
binary signals digital signals having only two possible levels of
amplitude

xv
 binary technology where the numbers used are represented with two
digits only, 1 and 0
broad-banding being able to operate over a wide range of
frequencies
capacitance the ability to store electric charge
capacitor electrical component used to store an electrical
charge
carrier wave a periodic signal at some desired transmission
frequency used as the basis for a modulation
scheme
channel a link in a telecommunications network through
which signals propagate
channel capacity a measure of the amount of information that can be
sent over a communications channel without error
coaxial cable two concentric conductors separated and
surrounded by an insulating material
coding the process of modifying or adding to the
representation of information (for security, error
protection, compression, etc)
coherer a device to detect the presence of radio frequency
(RF) energy and thus receive a wireless pulse
conductor a material that has low resistance to the flow of
electricity
current the rate of flow of electricity through a conductor
data compression the process of reducing the amount of data in a
message without significantly altering the
information content of the message
data packets short segments of a digital message that are
combined with additional information (such as
source and destination addresses, packet number
and priority) to enable sending as individual sub-
messages across a packet switched network
datagrams see data packet
demodulation the process of shifting the information content of a
modulated signal back to baseband
demodulator a circuit designed to implement a particular
demodulation scheme
development the drawing of the true flat shape of an object, often
the flat shape of sheet metal ducts

xvi
digital signal a signal that can take on only a finite number of
possible amplitudes, and that only changes
amplitude at discrete regular intervals in time
digital transmission the use of discrete signal levels to send information
diode an electrical component that only allows electrical
flow in one direction
direct current (dc) current that flows steadily in one direction
doping adding an impurity to a semiconductor so it forms
an n-type or p-type material
downlink the communications channel from a satellite to earth
electromagnet a piece of iron or steel that is made into a magnet by
having an electric current passed through wires that
are wrapped around it
electromagnetic the range of frequencies at which electromagnetic
spectrum signals may be transmitted and propagated
electromagnetic wave an invisible form of radiation that consists of
changing electric and magnetic fields light, radio
signals, microwaves are all electromagnetic waves
electromagnetism the phenomena of the relationship between electric
current and magnetism, for example, a magnetic
field is produced by moving electrons (electric
current)
electrostatics the study of electrically charged particles
error correction the process of discovering and rectifying errors
made during transmission
error detection the process of discovering whether an error has
been made during transmission
facsimile an exact copy; a method of transmitting pictures by
radio telegraph
fibre optic a clear, flexible pipe, commonly made in glass,
that carries light pulses
freehand drawing the drawing of engineering details without the use of
instruments all drawing standards should be
applied where possible
frequency the number of complete cycles of a signal in a fixed
time, usually in one second
frequency division a multiplexing scheme in which users are allocated
multiplexing their own frequency bands

xvii
 frequency modulation a modulation scheme in which the information to be
transmitted is contained in the instantaneous
variations in the frequency of a modulated carrier
wave
frequency shift keying a frequency modulation scheme in which the
message signal is a digital signal
geostationary a term used in conjunction with satellite technology
to indicate an orbit around the earth above the
equator that is the same as the rate at which the
earth spins on its axis; a satellite so-positioned will
appear stationary with respect to the earth
graded index fibre type of fibre optic where the refractive index of the
core changes from the centre outwards
guided medium a medium for propagating electromagnetic signals
that requires a physical connection between
transmitting and receiving ends
hardwired connected by a solid medium, for example cables,
wires; not wireless as with transmission through
the air
information a measure of the intellectual value of a message
based on expected probabilities of the message
being correct
infrared signal electromagnetic signals at frequencies just below
the visible light spectrum
infrastructure buildings or permanent installations, for example,
power poles, transmission wires, that are associated
with an organisation or a system
insulation an insulating layer normally applied over a
conductor
insulation resistance the resistance offered by insulation to an impressed
voltage
insulator a material that has very high resistance to the flow
of electricity
integrated circuit large numbers of transistors, diodes, capacitors and
resistors formed and electrically joined on a single
slice of semiconductor material
laser stands for Light Amplification by the Stimulated
Emission of Radiation and is a device for producing
a high intensity beam of visible light; the light
produced is of a single frequency and wavelength
light emitting diode abbreviated to LED is a diode that emits light when
electricity flows through the component, used
instead of globes

xviii
mains wiring electrical conductors used to distribute electrical
power
megger testing a non destructive test used to assess the insulation
on a cable or electrical installation
message signal a baseband signal containing information to be
transmitted (usually in the context of modulation)
microwave signals electromagnetic signals at frequencies in the 240
GHz range
modulated the changed characteristics of a carrier wave due to
the addition of a signal wave that creates a
composite of the two waves
modulated carriers set frequency waves used to carry information
within signal waves broadcast with them
modulation the process of shifting a baseband signal to another
range of frequencies to facilitate transmission
efficiency
modulator a circuit designed to implement a particular
modulation scheme
morse code a code linking numbers and letters to sequences of
dots and dashes for transmission by telegraph or
other signal system
multimeter a meter that can be used to measure voltage, current
and resistance
multimode type of fibre optic that allows the flow of many
modes of light

multiplexing the simultaneous transmission of several signals

along a single path without any loss of identity of
an individual signal
n type a semiconductor in which current flow is caused by
the movement of electrons
noise a component of a signal that is undesirable and/or
unavoidable
optical fibre a filament of glass surrounded by mechanical
protective materials
oscilloscope a device for measuring and displaying the voltage
of a signal as it varies with time
p type a semiconductor in which current flow is caused by
the movement of holes
packet switched a network in which data packets are sent via any
network suitable path from sender to receiver

xix
 packetisation the process of breaking a long digital message into
smaller parts, each of which can be sent
independently from other packets making up the
total message
PCB stands for Printed Circuit Board which has an
insulating polymer base layer and copper tracks on
the top surface
period the time taken for a periodic signal to complete one
cycle
periodic (signal) a signal that is repetitive in time, such as a sinusoid
or a triangular wave
phase modulation a modulation scheme in which the information to
be transmitted is contained in the instantaneous
variations in the phase of a modulated carrier wave
phase shift keying a phase modulation scheme in which the message
signal is a digital signal
plain text the body of a message prior to encryption, and
recovered after decryption
p-n junction the joining together of a p-type and an n-type
semiconductor
protocols the programming rules by which networks are able
to connect into the Internet
quantisation the process of rounding a measured amplitude to
the nearest allowable ampitude in a finite set of
allowable amplitudes
quaternary signals digital signals having only four possible levels of
amplitude
radio the use of air and free space for propagation of
unguided electromagnetic signals
regeneration the process whereby a digital signal corrupted by
noise can be reconstructed as a noise-free signal
repeater stations installations that receive messages, then re-emit
them at higher energy to ensure that signal strength
is maintained and the signal does not fade out
resistivity a measure of the ability of a material to resist the
flow of current, for example, copper has a lower
resistivity than aluminium; the resistance offered by
a wire in a circuit is determined by the resistivity of
the material of which it is made, its length and its
thickness
resistor electrical component used to restrict electrical flow
sampling the process of measuring the amplitude of a signal
at regular intervals (in time or space)

xx
semaphore a signal system achieved with flag waving
semiconductor a material between conductors and insulators that is
used to control the flow of electrons in transistors,
diodes, integrated circuits and similar electronic
devices
signal to noise ratio the ratio of amplitudes of a (desired) signal and
noise
silicon an element with four valence electrons that is
commonly used as the basis for semiconductor
devices
single mode type of fibre optic that allows the flow of a single
mode of light
step-index fibre type of fibre-optic where the refractive index is
constant in the core and it steps to a different lower
value in the cladding
ternary signals digital signals having only three possible levels of
amplitude
time division a multiplexing scheme in which users are allocated
multiplexing their own time slots
transistor a semiconductor electronic device used to switch or
amplify an electric signal
transition piece a short section of sheet metal ducting used to join
different shaped ducts
triangulation a system of dividing a transition piece into
triangular segments for the purpose of drawing the
development of the piece
true length the actual length of the line, rather than the apparent
length
twisted pair a pair of insulated wires that are twisted around
each other so as to reduce the amount of noise that
is induced into the conductors
twisted pair cable a bundle of twisted pairs of wires in a common
sheath
unguided medium a medium for propagating electromagnetic signals
that does not require a physical connection between
transmitting and receiving ends
uplink the communications channel from earth to a
satellite
valence electrons electrons in the outer shell of an atom that are
generally involved in forming bonds between atoms
in metals they are relatively loosely held and can
move from atom to atom

xxi
 valve a device using the passage of electrons across
charged plates to produce the same electronic
characteristics now achieved with semiconductors
virtual circuit network a network in which ordered data packets are sent
via a specific path through a network
voltage the potential difference between two points in a
circuit measured in volts
waveguide a guiding medium used for microwave signals
wavelength the distance in space between identical points of a
periodic signal

xxii
Directive terms

The list below explains key words you will encounter in assessment tasks
and examination questions.

account account for: state reasons for, report on;

give an account of: narrate a series of events or
transactions

analyse identify components and the relationship between

them, draw out and relate implications

apply use, utilise, employ in a particular situation

appreciate make a judgement about the value of

assess make a judgement of value, quality, outcomes,

results or size

calculate ascertain/determine from given facts, figures or

information

clarify make clear or plain

classify arrange or include in classes/categories

compare show how things are similar or different

construct make, build, put together items or arguments

contrast show how things are different or opposite

critically add a degree or level of accuracy depth, knowledge

(analyse/evaluate) and understanding, logic, questioning, reflection
and quality to (analysis/evaluation)

deduce draw conclusions

define state meaning and identify essential qualities

demonstrate show by example

xxiii
 describe provide characteristics and features

discuss identify issues and provide points for and/or against

distinguish recognise or note/indicate as being distinct or

different from; to note differences between

evaluate make a judgement based on criteria; determine the

value of

examine inquire into

explain relate cause and effect; make the relationships

between things evident; provide why and/or how

extract choose relevant and/or appropriate details

extrapolate infer from what is known

identify recognise and name

interpret draw meaning from

investigate plan, inquire into and draw conclusions about

justify support an argument or conclusion

outline sketch in general terms; indicate the main

features of

predict suggest what may happen based on available

information

propose put forward (for example a point of view, idea,

argument, suggestion) for consideration or action

recall present remembered ideas, facts or experiences

recommend provide reasons in favour

recount retell a series of events

summarise express, concisely, the relevant details

synthesise putting together various elements to make a whole

Extract from The New Higher School Certificate Assessment Support Document,
Board of Studies, NSW, 1999.

Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

xxiv
Telecommunications engineering

Part 1: Telecommunications engineering

scope of the profession & engineering report
 Part 1 contents

Introduction..........................................................................................2

What will you learn?................................................................... 2

Scope of telecommunications engineering ....................................3

Current technology in the telephone network............................... 5

Current applications and innovations .........................................15

Health and safety issues ...........................................................22

Relations with the community ....................................................25

Legal and ethical implications....................................................27

Training and careers in the profession .......................................28

Engineering report............................................................................31

Structure of an engineering report..............................................31

Sample report ..........................................................................33

Exercise .............................................................................................41

Progress check .................................................................................43

Exercise cover sheet........................................................................45

Part 1: Telecommunication engineering scope of the profession and engineering report 1

 Introduction

Telecommunications is the transmission of voice, data and other

information over extended distances.

The telecommunications industry covers a wide range of systems and

technologies. The industry includes among other areas; radio, television,
telephone, satellite communications, microwave and computer networks.
In this section on the scope of telecommunications and in the history
section you will consider aspects of these technologies.

What will you learn?

You will learn about:
nature and scope of telecommunications engineering
health and safety issues
training for the profession
career prospects
relations with the community
technologies unique to the profession
legal and ethical implications
engineers as managers
current applications and innovations.

You will learn to:

define the responsibilities of the telecommunications engineer
describe the nature and range of work done in the profession
examine projects and innovations in the telecommunications
profession
analyse the training and career prospects within telecommunications
engineering.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

2 Telecommunications
 Scope of telecommunications engineering

Engineers involved with telecommunications work in one of the most

rapidly expanding and complex fields of engineering. When you
consider the range of telecommunications products available you will
realise why engineers involved in this field tend to specialise in one
general area. There is just too much to know. This is especially so when
designing software that must conform to the many protocols and
standards that are required by international conventions and agreements.

One engineer who was interviewed when compiling this unit had spent
15 years as part of a university team that was developing and improving
the methods for producing communications grade optical fibre. The
complexity of this task is not readily apparent but he indicated that the
work involved was both challenging and varied throughout his time on
the project.

Examples of general engineering areas that a telecommunications

engineer could be involved in include:
transmission media the material or media in which the signals are
carried or transmitted
transmission and receiving equipment the equipment which
actually converts and transmits the telecommunications signals
transmission technology the method and protocols by which the
signals are encoded and decoded
switching systems the method of connecting and recording the
connection of one piece of terminal equipment to another ( and
calculating those terrific phone bills that arrive every three months).

Telecommunications engineers may be involved in projects which

include:
Research both pure research and research aimed at developing
commercial products. The principle of fibre optic communication
was proposed more than 50 years before scientists at Corning glass
developed a glass of high enough optical purity to make commercial
optic fibre a reality.

Part 1: Telecommunication engineering scope of the profession and engineering report 3

 Design of equipment and systems many engineers working in the
telecommunications field are electrical or electronics engineers.
Their specialist knowledge of electronics and power enable them to
design, develop and test the equipment needed to transmit voice and
data over long distances. Other engineers, specializing in software
design and computing, develop the programs and code required to
implement the protocols and encoding required for modern
telecommunications systems.
Supervising the manufacture of equipment this involves managing
teams of skilled and unskilled workers, maintaining manufacturing
standards and coordinating with component suppliers to maintain
production schedules.
Installation and commissioning of equipment and systems in this
area the engineers with specialist knowledge are employed
primarily for their skills as managers. They will be involved in co-
ordinating large teams of people to install, test and commission
complex equipment. Most often this has to be done to a tight time
schedule. High levels of organizational and interpersonal skills are
essential in this area.
Maintenance and upgrading of installed systems again the engineer
is primarily employed as a manager. Good maintenance requires
strict adherence to scheduling and coordination of a wide range of
personnel.
Sales, tender preparation and marketing of telecommunications
systems the complexity of telecommunications systems dictate that
the personnel who sell and purchase equipment/systems in this field
need to possess a high level of technical knowledge. Engineers and
software designers who have worked on the technical aspects of
telecommunications systems will have highly developed technical
knowledge and expertise.

4 Telecommunications
 Current technology in the telephone
network
In this section you will examine the current telephone network and the
transmission media and technology that telecommunications
professionals deal with.

Transmission media
When you complete the history section you will realize that from the
time of Alexander Graham Bell until the late 1970s the components used
in the public telephone system have changed very little in their principle
of operation and have evolved relatively slowly. The industry name for
the public phone system is the public switched telephone network or
PSTN.

The earlier plain old telephone system (POTS) used solid copper wire
twisted in pairs to run from the subscribers home to the closest
telephone exchange. Many such pairs were present in a cable and it is
technically known as unshielded twisted pair (UTP) cable. This is very
similar to UTP cable that is currently used to connect computers together
in local area networks (LANs).

At the telephone exchange the wires were directly connected to an

electro-mechanical switching system that then directly connected the
subscriber to the desired line. This usually meant connecting to at least
one other telephone exchange and then continuing on UTP to the
telephone being dialed. A continuous, hardwired electrical circuit was
formed between the two telephones involved. This is known as circuit
switching and was in operation in Australia for over 100 years. Some
components of this system are still in operation today. Unfortunately,
twisted pair is subject to attenuation (loss) as the length of the wire is
increased. Distances of over 3000 metres tend to attenuate the signal
significantly. The shorter the copper line the higher the quality of the
signal that reaches the exchange. For longer distances, amplification
(boosting) of the signal was required at regular intervals to maintain the
signal quality.

Before we go on, list any other ways that you could transmit the signals
between exchanges or over long distance without this loss of quality.
__________________________________________________________
__________________________________________________________
__________________________________________________________

Part 1: Telecommunication engineering scope of the profession and engineering report 5

 Did you answer?
Some of the ways you can transmit signals between exchanges over long
distances without loss of quality include:
coaxial cable
radio transmitters
microwave
laser beams
satellites
optical fibre.

As it turns out, virtually any other media and transmission method works
better than wire but unfortunately they were not available in the 1890s.
Currently a number of systems are available and are used to transmit
signals between exchanges. They include:
coaxial cable
optical fibre
wireless microwave, satellite and cellular
digital encoding rather than analogue.

Coaxial cable
Coaxial cable consists of a single conductor running down the axis of the
cable surrounded by a dielectric (or insulating) layer. A continuous
conducting shield covers the cable. A protective insulating layer is
placed over the shield. The shielding material prevents high frequency
radiation from leaking from the cable. Coaxial cable is also used
extensively in the cable television industry to carry dozens of TV
channels on a single cable. This material is therefore said to have a high
bandwidth compared to plain copper.

Single solid conductor

on the central axis

Insulating layer Conducting material forming a

continuous outer shield

Figure 1.1 Construction detail of coaxial cable

6 Telecommunications
 Optical fibre
Optical fibre is being used increasingly in telecommunications and
computing networks. Optical fibre uses the internal reflection of light
down a light guide to transmit signals. The light guide is made from a
glass core enclosed in a glass cladding layer with a different refractive
index. Optical fibre has a much higher bandwidth than either UTP or
coaxial cable.

In creating the first commercially viable optical fibre, scientists and

engineers had to produce an incredibly pure glass. To put this in
perspective, if you want to transmit light along a one kilometre long
optical fibre then you have the equivalent of transmitting light through a
pane of glass which is one kilometre thick. Even more mind blowing, a
100km transmission is the equivalent of having a glass window pane
which is 100 km thick.
Light beam reflected Protective acrylate coating
along the core

Core material manufactured Cladding material with lower

from high purity glass refractive index than the core

Figure 1.2 Light reflected along the glass core of an optical fibre.

The optical fibres developed in the 1970s only retained 1per cent of the
light transmitted after traveling one kilometre. This equates to an
attenuation of 20 decibels per km (dB/km). This was regarded as a great
success. Today attenuation rates of 0.25 decibels per kilometer are
common. It is now possible to transmit beyond 100 km in optical fibre
without amplification.

You will note the use of the term decibel which is abbreviated to dB.
This term is often used to describe the gain or attenuation of signals in
electronics. Decibel scale is logarithmic and as such yields a compressed
measuring scale for values that can vary widely.

The general formula for calculating decibel gain or loss is

dB = 10 x log (gain or loss)

In early commercial optic fibre only 1% of the signal traveled the full
one kilometre. The attenuation or loss was therefore 100 times. The
attenuation in decibels can be calculated by:

Attenuation dB = -10 x log 100 = - 20 dBs

Part 1: Telecommunication engineering scope of the profession and engineering report 7

 The bandwidth of optical fibre is phenomenal. This is because the carrier
waveform is light and the frequency of light is much higher that radio
waves. At the time of writing the transmission speeds for optical fibre
were quoted as high as 9.9 Gbps. This equates to the entire 15 volumes
of Encyclopedia Britannica in far less than one second.

Optical cable is now commonly used to span great distances between

exchanges and even between countries. Engineers in Australian
companies such as Alcatel (formerly Standard Telephone and Cable)
design and manufacture undersea optical fibre cable which carries
telephone traffic world wide.

Initially the telecommunications engineers and planners had envisaged a

system where optical fibre was delivered right to the home. In the
industry this is known as fibre-to-the-home (FTTH). This has recently
been seen as overkill both in bandwidth capacity and in cost. The current
planning involves hybrid systems that utilise fibre to the neighborhood
(FTTN) then use cable or UTP to deliver the signal to the home. In the
innovations and current technologies section you will learn about a
specialised modem system that allows much higher speeds on standard
UTP copper wire.

Wireless technology
Wireless technology, as the name suggests, does not use cable or wires to
connect between exchanges and or telephones but instead uses radio
frequency broadcasting to transmit the signal. This can considerably
reduce the need for costly hard wired infrastructure while
simultaneously increasing the mobility of some users. Wireless
broadcasts are commonly made in the microwave end of the
electromagnetic spectrum.

The application of wireless technology is varied. The common

applications include ground based microwave networks, cellular phone
systems, geo-stationary satellites and low earth orbit satellites.

Microwave frequency transmissions travel in straight lines. Unlike lower

frequency radio waves they do not refract in the earths atmosphere or
bounce off the ionosphere to any significant degree. Microwave
communication is essentially line of sight. If you cannot see the
transmitter you cannot pick up the signal.

The ground based microwave systems have a series of microwave towers

spaced at regular intervals across the countryside. These towers have line
of sight to each other. Each tower receives and then re-transmits signals
from other towers that it can see. These towers are therefore called
microwave repeaters. This system is used to transmit signals between

8 Telecommunications
 remote telephone exchanges and is commonly used in semi-remote areas.
You will often see these towers with their small parabolic dishes on top of
tall mountains and high ground. The NSW railways and electricity
authorities have their own microwave communications networks.

Why do you think these towers are placed on tall mountains?

Figure 1.3 Microwave towers

__________________________________________________________

__________________________________________________________

Did you answer?

Placing towers on high points gives the longest possible straight line (line of
sight) transmitting distance because there are no objects in the way.

Geo-stationary or geo-synchronous satellites

Geo-stationary or geo-synchronous satellites hold a set position above
the earths surface, rotating at the same angular velocity as the earth. A
geo-stationary that was on station above say Dubbo would hold that
position continuously and only vary if its navigation system was
reprogrammed for a new location.

These satellites are stationed approximately 37 200 kms from earth.

Radio waves propagate at the speed of light. The combination of the
satellites distance from earth and the finite speed of the radio signal
introduces a very small delay between the transmission of the signal and
the arrival of the signal back at earth. This delay is acceptable for data
communications and some international voice communications but is not
regarded as satisfactory for cell phone type communications. If you have
seen the movie Apollo 13 you may recall that it took one or two
seconds for the transmissions from the Apollo 13 module to reach earth.

37 200 km

Earth Dubbo

Geo-stationary
satellite
Figure 1.4 Geo-stationary or geo-synchronous satellites have a time delay of
around a quarter to half a second due to their distance from earth

Part 1: Telecommunication engineering scope of the profession and engineering report 9

 Telstra is a member of the INTELSAT and INMARSAT groups which
operate a large number of geostationary satellites.

Calculate the time delay that you would expect for a signal to reach a
geo-stationary satellite then return to earth. Assume that the
displacement of the satellite is 37 200 km from the surface of the earth
and that the speed of light is 3 x 108 m/s.

Did you answer?

velocity (V) = displacement (S) S = 37 200 km

time (t) 6
... t = S = 37.2 x 10 m
V 8
V = 3 x 10 m/s
= 37.2 x 106m
3 x 10 8 m/s
= 0.124s
t
one way = 0.124 sec
t
both ways = 2 x 0.124 sec = 0.248 sec

ie about 1/4 sec out and back

Cellular phones
Large numbers of people now own and operate mobile phones. These
mobile phones are also known as cellular phones.
Supposing that a single tower was placed in the center of Sydney to
transmit and receive to and from all the phones owned by subscribers in
Sydney. The tower would simply be overwhelmed by the number of
subscribers trying to call.
To eliminate this problem the metropolitan area is divided into cells a
few kilometres across, hence the name cellular phone. Each cell has a
base station (mobile phone tower) operating at a different set of
frequencies to nearby cells. The towers operate on low power outputs so
that the operating frequencies can be re-used at other locations. When a
subscriber moves from one cell to the next the call is simply transferred
or handed on to the base station associated with the next cell.

10 Telecommunications
 Base station

Cell Hand on point

Figure 1.5 Four base stations co-ordinating calls from two mobile phone units
in a cellular network

Originally Australia adopted an analogue transmission system. Analogue

systems are fabulous for voice communication but fail to offer all the
extra bells and whistles of digital systems. To be really cynical you
could say that they dont offer all the money making options that digital
phones provide. As well, analogue transmissions require more of the
available frequency bandwidth per channel and thereby make less
efficient use of the narrow frequency band available. The analogue
cellular telephone network was closed down in Australia in 2000.

Digital mobile phones use the global system for mobiles or GSM
transmission system. The digital nature of the transmission means that
both data and voice are readily transmitted and that a wide range of
features can be included.

List four features available on a modern digital mobile phone, for

example, personalised ring tone.
1 _______________________________________________________
_______________________________________________________
2 _______________________________________________________
_______________________________________________________
3 _______________________________________________________
_______________________________________________________
4 _______________________________________________________
_______________________________________________________

Part 1: Telecommunication engineering scope of the profession and engineering report 11

 Did you answer?
Some of the features available on a modern digital phone include:
call forwarding
voice recognition dialing
infra red links
stored numbers
digital games
messaging systems.

When the analogue phone network was decommissioned in Australia, the

coverage of GSM digital mobile phones was inadequate. This was
especially so in rural Australia. The government allowed a new system
to be introduced into the mobile network to supplement coverage in rural
areas. This system is called code division multiple access, more
commonly known as CDMA. Now you need two telephones, a CDMA
to make calls in rural Australia and a GSM digital to make calls in
metropolitan Australia. See what happens when politicians are asked to
make a sensible decision!

Low earth orbit satellites

Low earth orbit satellites are an emerging technology. Low earth orbit
satellites orbit about 1500 kms above the earths surface, consequently
they move quite rapidly across the sky and have no noticeable time
delays. At this time, several companies are developing plans for LEO
satellite systems. These companies include Teledesic, Globalstar,
Odyssey and Motorola (Iridium). It is conceivable that not all these
systems will be introduced or succeed.

In a low earth orbit system the satellites are equivalent to mobile

telephone towers in the sky. Instead of the telephone user moving from
one cell to another, the cell associated with a particular satellite moves
with the satellite across the surface of the earth. As one satellite passes
below the horizon a new satellite is available so the telephone user can be
handed on. The Globalstar system, for example, will require forty eight
satellites to adequately cover the earth.

12 Telecommunications
 Low earth orbit satellite
1500 km above the surface

Departing satellite

Earth

Figure 1.6 Low earth orbit satellites need to hand-off to other satellites before
they move over the horizon

What do you think is the advantage of low earth orbit satellites over
geostationary satellites?
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

The short distance, 1 500 km, means that there is no delay noticeable by the
user. It is instant, therefore it is better for voice communications.

Transmission technology
In the early 1980s Telecom Australia (now known as Telstra) began a
revolutionary change in the technology used to transmit voice and data
between telephone exchanges. Up until this time all the signals
transmitted on the telephone network were analogue in nature. This was
perfectly adequate for voice communications but the forward thinking
engineers at Telecom were already planning for the digital revolution that
was to descend on them. Telecom engineers and planners had decided to
implement a fully digital switching and transmission system between
telephone exchanges. This system is now able to be delivered right up to
the subscriber in the form of ISDN but it is very costly.

An analogue connection on single copper wire needs to be maintained

continuously during a conversation and normally only one conversation
is able to be carried out on that particular line. This is very wasteful use
of expensive resources especially between exchanges. The situation can
be improved by using a transmission media such as optic fibre where

Part 1: Telecommunication engineering scope of the profession and engineering report 13

 multiple channels can be carried on a single fibre. However, the
connection must still be continuously maintained.

With a digital telephone exchange, the connection between exchanges is

a virtual connection. It is not a hard wired connection. The
connection is linked only when data is being sent or received. Also, all
the data being transmitted is digital. This includes the voice
communications components.

Well how can this be so?

The fundamental process involved in digital transmission is a form of

packet switching.

Packet switching in telephone networks operates like this:

you dial your number and the computer at the telephone exchange
notes down where you want your voice to be sent to
you then speak into your telephone and your voice is transmitted via
copper lines to the telephone exchange
the computer at the exchange then samples your voice at about 8 000
times a second and assigns it a digital number each time that is, it
is quantising your voice ready for digital transmission
the computer then bundles up the sampled conversations or data into
an electronic packet, this packet is addressed and error correction
codes are attached
the packet is then sent off to the destination exchange where it is
digitally unpacked, converted back to analogue and then sent via
virtual connection to the destination telephone line
the speed at which modern telecommunications computers operate is
so fast that the user is totally unaware that this process is happening.

A simple analogy for this process is when someone moves house. First
all the items in each room are packaged and labeled according to their
destination rooms. The packages are placed into the moving van in any
order that suits the person loading the van. The van drives off. At the
destination the van is unloaded and the packages are taken to the rooms
that match their labels and unpacked.

14 Telecommunications
 UT
P DN
Data packets in transit IS

UT
DN P
IS Digital Digital
Exchange Exchange
A B

Figure 1.7 A digital network using packet switching between telephone

exchanges (note that the UTP lines are analogue and the ISDN
lines are digital between the telephone exchange and end user)

Two companies have supplied digital telephone exchanges for the current
Telstra network. Ericsson have supplied the AXE digital exchanges and
Alcatel have provided the System 12 digital exchanges. The engineer
featured in the Engineering report at the end of this section was involved
in the development and manufacture of the System 12 exchanges in
Australia.

Telecommunications engineers may be involved in any aspect of the

above areas. They may specialise in designing wireless transmitting
equipment, developing software to run digital mobile telephones,
supervising the manufacture of telephone exchanges or any one of the
multitude of tasks needed to keep the telephone network running and up
to date.

If you have access to the Internet and wish to find out more about
telecommunications technology, both leading edge and historical
information, then the International Engineering Consortium (IEC)
have an excellent tutorial section at: <www.iec.org/tutorials>
(accessed 04.12.01).

Current applications and innovations

You will now learn about some of the emerging technologies in
telecommunications engineering.

Telecommunications technology is emerging at an incredible rate. To

attempt to put down on paper and predict the direction of this technology
is a risky business. In fact, by the time that you read this some of the
technologies described here may have already been discarded.

Currently two distinct but related concepts are driving telecommunications

development. These concepts are broad-banding and convergence.

Part 1: Telecommunication engineering scope of the profession and engineering report 15

 Broad-banding
Broad-banding is related to bandwidth and is primarily concerned with
transferring as much data as possible through a transmission system in as
short a time as is possible. The need for broad-banding comes from the
ever increasing demands of industry and domestic users for high speed
data transfers. This is often associated with computer networks such as
wide area networks (WANs) and the internet.

For example, internet web pages now often contain large amounts of
photographic material, video clips, music clips and even full length
movies. These graphics images require very high rates of data
acquisition and currently take long periods of time to download. Two
solutions suggest themselves. Compress the image data and/or increase
the rate at which data can be transmitted.

Compression solutions are constantly being refined by software designers

in the internet industry. Compression formats now exist for photographs,
video, music and other types of files. Compression reduces the file size
required to store the image or sound.

List one common compression format for each of the following file types:
music, video and photographs.
Photograph: ________________________________________________
Video:_____________________________________________________
Music:_____________________________________________________

Did you answer?

Photograph JPEG, Compressed TIFF, GIF

Video MPEG
Music MP3.

The development of methods for increasing data transmission rates is the

domain of the telecommunications engineer. Two areas currently being
implemented are ATM and ADSL.

ATM or Asynchronous Transfer Mode is a refinement of earlier packet

switching. Unlike packet switching it is designed for high performance
multimedia communications. ATM is essentially a protocol or an
internationally agreed way of transferring data. It is interesting to note
that another protocol that you may be familiar with is also out there
competing with ATM. That protocol is the IP protocol that you may have
associated with Internet communications. You will have most likely

16 Telecommunications
 seen it written as TCP/IP. Currently, engineers with several large
telecommunications companies are developing and optimizing ways of
transmitting voice over these two protocols.

Of more interest to the average home Internet user is the implementation

of ADSL or asymmetric digital subscriber line. You will recall that the
copper lines running from your house to the closest telephone exchange
are not very good for transmitting data. In fact, if you currently had a
standard 56k modem you would be extremely lucky to get anywhere near
that Baud rate on a continuous basis. The copper UTP telephone line is
the limiting factor.

ADSL is not a new telephone line but in fact a pair of extremely

sophisticated modems. One modem at the telephone exchange and
another modem at the end users premises. ADSL is promising data
transfer rates of up to 6 Mbps on 3 to 4 km of copper telephone line.
This is quite adequate for real-time watching of movies and listening to
music.

Digital
Telephone
UTP
Exchange
Home ADSL ADSL
computer Modem Modem

Figure 1.8 An ADSL modem pair set up to provide high speed data
transmission to the home of a subscriber

Another innovation made possible by digital exchanges is the intelligent

network. Intelligent networks use the computing technology now
associated with telephone networks to make intelligent decisions about
subscriber calls. For example, a home delivered pizza company may
have 25 outlets in Sydney. However, it has only one listed number in the
telephone directory. When you phone for a pizza, to help you get
through the hours of study that you are obviously putting in for your
HSC, a marvellous thing happens. The pizza outlet that answers is the
one that is closest to your home. The intelligent network has taken
your call and decided on the closest outlet then directed your call to that
point. Intelligent networks provide an array of value added services
such as call forwarding, prepaid calling facilities and call waiting.

Part 1: Telecommunication engineering scope of the profession and engineering report 17

 Convergence
This is a vast and expanding area. Until very recent times telephones
were used to place telephone calls, television stations broadcasted
movies, printing firms produced books, radio stations broadcast music
and computers were stand-alone business tools. All these
communications systems used different formats to store and transmit
their content. Earlier in this section you learnt that many devices that
were previously analogue are now available as digital devices: digital
telephones, DVD players, digital televisions, CD players and even
telephone exchanges. The data used by these digital devices can be
shared, provided that a common communications protocol is used.

At the same time a rather contrary change is occurring in transmission

systems. Media that were once delivered by wireless technology are
being delivered over wire cable and optic fibre, for instance cable
television and some radio. At the same time, traditionally hard-wired
technology, such as telephones, are rapidly moving into wireless
technology in the form of mobile phones.

The third factor that is coming into play here is the increasing speed of
computers and development of the Internet. The Internet has provided a
common protocol, that is TCP/IP. As you will recall IP (Internet
protocol) is a transmission protocol that can be used to move data across
telephone lines.

Broadcast and digital media convergence is the coming together of

telecommunications, television, computing, radio, music and the Internet.
Convergence builds from technologies we already love to use:
broadcast technology television and radio
the computer and internet
the telephone.

Convergence is an emerging concept. It is currently available to a

limited extent but its use should expand dramatically in the next five or
so years. For instance you can currently receive television on your
computer. You can also receive wireless internet by connecting your
mobile phone to your laptop. You have to admit though, that the time to
download and the overall quality is not that impressive.

1 List other examples of convergence that are currently available.

_______________________________________________________
_______________________________________________________
_______________________________________________________

18 Telecommunications
 2 A current technology that attempts to address the demand for
wireless internet is the WAP mobile phone. Indicate what the letters
WAP stand for and what a WAP phone does.
_______________________________________________________
_______________________________________________________
_______________________________________________________

Did you answer?

1 Interactive video on DVD and Web cams, for example @surfing beaches,
available on the Internet are other examples of convergence.
2 Wireless Application Protocol, that is WAP, can access a range of modified
Internet sites. However, the type and quality of the data is limited by the
capacity of the phone.

In its present form, WAP is quite limited in what it can achieve. WAP
will have to evolve into something more sophisticated and user
friendly otherwise it will be overtaken by some other currently
emerging technology. In Japan for instance, the DoCoMo companys
rival system i-mode had signed up 10 million users between
February 1999 to October 2000.

New Scientist, 21 October 2000.

You are now going to learn about two emerging and related technologies
both of which are associated with convergence but also incorporate a
large range of other systems. These technologies currently look like they
are going to succeed but this is by no means certain. These emerging
technologies are :
3G third generation mobile telephone
Bluetooth.

3G
3G mobile phones are the next generation of mobile phones. 3G will
have data rates which are 150 times faster than a WAP phone. It is
estimated that 3G will eventually achieve rates of 2 megabits per second.
This will give 3G equipment speed and capacity at broadcast level.
Applications can include direct Internet access, MP3 music on the move,
video phones and phone shopping. 3G telephones will be the first
telephone to fully exploit the Internet and broadband options.

Part 1: Telecommunication engineering scope of the profession and engineering report 19

 The significantly higher data rates available from 3G make another
feature possible; tracking or position location. Using a known listening
station the telephone network can assess the time for signals to travel to
and from a particular mobile phone and two or more known base
stations. These signals can then be triangulated to give the location of
the user within 5 metres. This could be very good for emergency
services if you were making a 000 call.
Base Station 1

Base Station 2
Phone

known
displacement

Listening
Tower

Base Station 3
Figure 1.9 The displacement of the 3G mobile telephone user is determined
by the time taken for the signal to reach the listening tower
compared to the time to reach the 3G mobile phone. The system
then simply triangulates displacements from the 3 base stations.

Bluetooth
Bluetooth is a communications standard and specification initially
proposed by Ericcson but now taken up by a range of large
telecommunications companies. It is a wireless technology designed to
communicate with devices at ranges up to 10 metres. The bandwidth
anticipated will be up to 720 kbps with a power consumption as low as
one milliwatt (mW). Bluetooth has been backed by an interest group
which includes Ericcson, Motorola, Intel, IBM, Nokia, Toshiba and
Lucent Technologies.

At this point you are probably thinking, what is the use of a

communications system that can transmit only 10 metres. You can talk
to someone at that range.

The Bluetooth module is quite small. At present the Ericcson unit is less
than 30 mm long. It is anticipated that the device will be placed inside a
wide range of computing and microprocessor controlled devices. These
could include standard telephones, 3G telephones, microwave ovens,

20 Telecommunications
 stereo systems, home computers, car stereo and vehicle and engine
management systems.

So what! Who wants to ring up their washing machine and discuss the
quality of laundry detergent or the likelihood of rain today?

Well as it happens very few people will want to do so. However, many
people will be interested in some other possibilities. With a Bluetooth
module installed in your new 3G mobile telephone, you are immediately
identified to all other Bluetooth modules within 10metres.

You leave for work in the morning and jump in the Bluetooth equipped
family car. The car seats adjust to suit your preset requirements and the
engine management system adjusts the engine and gearbox to suit your
driving style. The Bluetooth enabled air-conditioning sets itself to 23.5
degrees. As you left the house the dishwasher and washing machine
switched on. Their Bluetooth modules have been programmed to operate
these machines when you are not at home because you cannot stand the
sound of running water.

Later in the day you buy some new shoes and need some cash out. The
transaction is carried out using your mobile phone and PIN while
standing at the cash register of the supermarket. Just as you leave the
supermarket your telephone and the telephone of a person nearby beeps.
Via Bluetooth interaction, your telephone has just found another person
who loves restoring Datsun 200Bs. This scenario is already happening
in places such as Japan where i-mode devices are used to meet people
of similar interests. i-mode has been especially popular amoung young
people looking for like-minded friends.

Outline any other uses that Bluetooth technology could be put to in

everyday life.
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

Bluetooth technology could be used by business to market goods, for example,
you walk past a shop and your phone beeps, it announces a special on hockey
sticks in a nearby outlet your phone had hockey programmed in as one of
your interests.

Part 1: Telecommunication engineering scope of the profession and engineering report 21

 Health and safety issues
In this section you will learn about some safety issues related to the
telecommunications industry.

In previous modules you have discussed health and safety issues

associated with the manufacturing process and commercial activity. For
instance, in Aeronautical engineering, you considered the effects of dust,
noise and chemicals and the appropriate control measures for these
hazards. In this module you will be investigating some hazards which
telecommunications technology may present to both industry personnel
and the end user.

One of the most visible telecommunications technologies to emerge in

recent times is the digital mobile telephone. These units emit
electromagnetic radiation when transmitting. The emission levels from
digital mobile telephones are very low but the frequencies are in the 800
to 900 megaHertz range. This is quite a high frequency.

You may be aware of discussion in the media about the electromagnetic

radiation emitted by mobile telephones. Outline any details that you can
recall about these media reports.
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

There is currently debate about the level of risk associated with the use of
mobile phone handsets and base station towers. These devices transmit signals
in the 800/900 MHz range which may be harmful to human health.

If anything is agreed on about the dangers of radiation from mobile

telephones it is that there is no agreement about the level of hazard posed
by these devices. No study to date has proved a statistically valid link
between mobile telephone emission and cancer or other diseases in the
brains of telephone users. At the same time, some academics have
expressed concern about young people being subjected to excessive
mobile phone radiation and the possible effects on brain development.

A domestic microwave oven cooks food by utilising high frequency

electromagnetic radiation to excite the molecules in water, fats and
sugars. The frequency required to do this is 2.4 GHz.

22 Telecommunications
 Could you hazard a guess at the frequency used by Bluetooth modules?

You guessed it, 2.4 GHz. This is not the problem that it at first seems.
The power output is at present so low, one milliwatt , that no danger is
presented. However, if the manufacturers try to increase the range of
Bluetooth much beyond 10 metres, then problems may well arise.
Incidentally, there is some concern that leaky microwave ovens may
jam the Bluetooth signals in some houses. Ericcson have developed a
frequency hopping mode for Bluetooth which the company believes will
eliminate this possibility.

Read the following extract from a newspaper article, New mobile

networks could double radiation levels, then answer the questions below.

Part 1: Telecommunication engineering scope of the profession and engineering report 23

 New mobile networks could
double radiation levels
Julie Robotham
Medical Writer
New generation mobile phone much closer to those associated with
networks operating on the radio health effects than were television
spectrum sold off by the Federal transmission towers.
Government last month could emit However, Dr Black was happy with
more than twice as much radiation as the numbers and believed the proposed
other digital mobile phone towers, if a standard would be safe for mobile
new technical standard is adopted. phone users. He said it was essential
the community was fully informed on
The radio spectrum to be used by the so- how mobile phones might affect the
called 3G networks raised $1.17 billion human body, so that people could make
for the Government in a recent auction. an informed choice.
Telstra, Vodafone and Optus were among
six companies that bid successfully for the One such issue was the blood-brain
new frequencies. barrier, which usually prevented
medications from acting on the central
The 3G network towers would be nervous system. Some medical
allowed to generate electro-magnetic conditions and high fever could make it
radiation of 10 watts per square metre- more permeable, allowing drugs and
double the maximum allowed for most chemicals to affect the brain more
radio base stations in todays digital directly. Dr Black said that animal
networks- under new limits that could be studies were inconclusive as to whether
formalised this year. mobile phone radiation made the barrier
An interim standard, which lapsed two more leaky.
years ago, allowed only 2 watts per square Another member of the working
metre. group, electrical engineer
The proposed standard would allow Mr John Lincoln, said he was unhappy
mobile phones based on either technology with draft standards approach to the
to operate at up to 2SAR- a measurement issue of differential heating of areas of
of radiation absorption by the head and the body.
body. This is an increase of about 70 per
cent on previous limits. He said the standard was predicated on
the idea that the body could efficiently
The proposed relaxation of restrictions cool heated areas through the circulation
on mobile phone radiation comes at a of the blood. Mr Lincoln said he did not
time of unprecedented community believe the levels specified in the
concern about its potential dangers. The standard would be changed, but there
National Health and Medical Research was no science at this point of time to
Council has committed more than $3 suggest that these factors are safe.
million to scientists studying the effects of
radiation on brain function and cancer. Mr Keith Anderson, director of the
Australian Mobile Telecommunications
The working group devising the new Association, which represents phone
standard includes doctors, community manufacturers and network operators,
groups and union representatives, under said it was a complicated issue. We
the aegis of the Australian Radiation dispute the simplistic assertions that the
Protection and Nuclear Safety Agency. proposed standard will result in large
Members concede its safety margins are increases in exposure. The power of
very narrow. mobile phones will not be raised.
Dr David Black, an occupational and Julie Robotham, Medical Writer,
environmental physician at the University Sydney Morning Herald
of Auckland Medical School, said mobile
handsets were allowed to operate at levels

24 Telecommunications
 1 Why do you think that the government is proposing to increase the
transmitting power allowed on base station towers?
_______________________________________________________
_______________________________________________________
2 What is one medical concern associated with this level of
electromagnetic radiation?
_______________________________________________________
_______________________________________________________

Did you answer?

1 The government is proposing to increase the transmitting power allowed on
base station towers as a result of pressure from phone companies who have
paid very large sums for 3G spectrum.
2 Of medical concern is the break down of the blood/brain barrier by radiation
allowing harmful chemicals to pass into the brain more readily.

The debate about electromagnetic radiation is not the only safety issue
currently associated with the telecommunications industry. However, it
is certainly the most controversial issue at this time.

Relations with the community

In this section you will learn about relations between the
telecommunications industry and the community.

Relations between the telecommunications industry and some community

interests could be characterized as somewhere between cynical and
downright hostile. A number of issues have arisen in recent times. Some
community relations issues that have caused comment and debate
include:
The rollout of coaxial cables for cable television. Cable television
companies utilised the existing electric telegraph pole network to
deploy their thick, black coaxial cables throughout the suburbs in
metropolitan Australia. Many communities objected to this extra
and unsightly use of these poles and some local government councils
attempted to ban the placement of these cables. People claimed that
the cables affected the visual amenity of their streetscape.
The placement of mobile telephone towers in residential areas.
These units are both unsightly and pose a possible health risk. The
towers have been placed close to many residential areas including
schools. This has often been done without adequate community

Part 1: Scope of the profession and engineering report 25

 consultation. Many communities have protested vigorously about
the placement of mobile telephone towers.
The decommissioning of the analogue telephone network in the year
2000. This was a significant problem in rural areas where the low
powered GSM digital phones lack suitable range. People in rural
areas have had to throw away their analogue handsets and then
purchase CDMA handsets. Subscribers in semi-rural areas often
have to purchase both a GSM digital and a CDMA to obtain
adequate coverage.
The high rate of theft of digital mobile telephones combined with the
telecommunications industrys reluctance to develop systems to
decommission stolen telephones. From a telecommunications
engineering perspective, this can be achieved by utilizing the
handsets IMEI number.
The quality of telephone services and internet provision in rural
Australia. The ability to access internet services at similar quality
and cost to city subscribers is an ongoing concern of country
subscribers. These people often have to pay higher prices for lower
quality services.

Figure 1.10 A mobile telephone tower

Would you like one of these put at the end of your backyard?

Telecommunications engineering scope of the profession 26

 Legal and ethical implications
In this section you will learn about the legal and ethical considerations of
telecommunications engineers and the products that they develop.

A large proportion of the engineers engaged in telecommunications

engineering are electrical engineers specialising in telecommunications.
Professional engineers usually belong to a professional association. The
Institute of Electrical and Electronic Engineers or IEEE is an
international association for professional electrical engineers. The IEEE
organisation has a professional ethics committee which has developed a
code of ethics which the IEEE expect all engineers affiliated with the
institute to follow.

Listed below are some selected items from IEEEs code of professional
behaviour:
To accept responsibility in making engineering decisions consistent
with the safety, health and welfare of the public, and to disclose
promptly factors that might endanger the public or the environment
To avoid real or perceived conflicts of interest whenever possible,
and to disclose them to affected parties when they do exist
To improve the understanding of technology, its application , and
potential consequences
To be honest and realistic in stating claims or estimates based on
available data
To reject bribery in all its forms.
The expectations listed above indicate that engineers are expected to
display a great deal of integrity in their day to day dealings and decisions.

The emerging technologies associated with mobile phones present a

number of legal and ethical problems.

Currently the Finnish government is investigating the use of mobile

telephone SIM cards to act as personal identification. The phone and
card could then be used for cashless transactions and for situations
where personal identification is required. However the high rate of
theft and simple loss of the telephone handsets will not assist the
acceptance of such a system by the general population.

New Scientist, October 21, 2000

The Finnish government also envisages a large amount of other personal

data being linked to this system via a database. This brings into play the
larger issue of privacy and security of data. The general public is not
likely to feel comfortable with such a system.

Part 1: Scope of the profession and engineering report 27

 Another issue associated with the emergence of 3G mobile telephones
is the ability of the phone company to track the current user. This will
be of benefit to the emergency services such as ambulance and police
when a 000 call is made but no address is supplied. It will also be
useful in tracking down lost and stolen telephones.
New Scientist, October 21, 2000

Ethical questions that arise from this development include:

Who should have access to the tracking capabilities; ambulance,
police, private investigators, parents or debt collectors?
What legal process should someone wanting to track the phone have
to follow?

Clearly, as sophistication and speed of technology increases, engineers,

telephone companies and government will need to closely examine the
extent to which technology impinges on peoples lives. They must then
make ethical decisions about the use of this technology.

Training and careers in the profession

As stated previously, most engineers employed in the
telecommunications industry have a background in electrical engineering
or software engineering. These types of engineering and computing
courses are offered by most of the large Australian universities.

Engineering courses are offered as undergraduate courses. In some

institutions, post-graduate extension courses such as diplomas and
masters degrees can be used to enhance engineering and science degrees.
Universities such as the University of NSW, Sydney University and the
University of Technology Sydney offer engineering degrees leading to
employment in the telecommunications industry.

Sydney University offers Bachelors of Engineering in Telecommunications

Engineering, Software Engineering and Electrical Engineering.

The University of NSW offers a Bachelor of Electrical Engineering with

the ability to specialise in communications.

In relation to specialising in communications, the UNSWs website states

that:

the activities of this department relate to all aspects of theory and

applications for a broad range of systems such as telephone and data
networks, radio and television broadcasting, satellite and deep space
applications.

Telecommunications engineering scope of the profession 28

 The department carries out advanced research in digital
communications, microwaves and antennas, optical communications
(including the design and manufacture of lasers and optical fibres),
signal and information processing and satellite mobile
communications.

In describing the possible roles of an electrical engineer the site indicates

that:

an electrical engineer may be responsible for research, design,

manufacture and operation of:

Communication systems; satellite, microwave, optical

Telecommunications
Broadcasting; television and radio

<www.eet.unsw.edu.au/programs/programs.html>

As was the case with Aeronautical Engineering, the courses have a very
high level of mathematics. Electrical engineers need to be able to carry
out difficult mathematical analyses of circuits and make predictions
based on complex mathematical models. The mathematical subjects to be
studied include: Vector calculus and complex variables, Fourier series
and differential equations and Matrix applications. Any student
contemplating these courses should be competent in high level
mathematics.

The rapidly expanding nature of telecommunications engineering means

that career prospects are very good and starting salaries for recent
graduates are very competitive.

If you have access to the Internet visit the following sites for further
information on telecommunications:
<www.voicendata.com/aug98/milestone.html> (accessed 04.12.01)
<www.uow.edu.au/informatics/ > (accessed 04.12.01)
<www.uws.edu.au/seid/programs/engineering/engineering.html >
<www.cit.uws.edu.au > (accessed 04.12.01)
<www.ee.newcastle.edu.au/undergraddesc.html > (accessed 04.12.01).

Part 1: Scope of the profession and engineering report 29

Telecommunications engineering scope of the profession 30
 Engineering report

In the engineering profession, an engineering report:

outlines the area under investigation
analyses available data
draws conclusions and/or proposes recommendations
acknowledges contributions from individuals or groups
documents sources of information
includes any additional support material.

Structure of the engineering report

This engineering report varies from the previous reports in that you will
be compiling a report about an individual involved in one area of the
telecommunications engineering industry. Previously you have reported
on a product, innovation or current project. For this section you will need
to interview a person involved in the telecommunications industry at a
technical level. It would be preferable that this person be a professional
engineer. However, this may be difficult in some rural or isolated
communities.

The engineering report will include the following sections:

Title

The title page gives the title of the report, identifies its author/s and gives
the date when the report was completed.

The abstract

The abstract is a concise summary of the report. The purpose of the

abstract is to allow a reader to decide if the report contains information
that is relevant to their needs. The abstract should be no more than two
or three paragraphs, and shorter if possible.

Part 1: Scope of the profession and engineering report 31

 The introduction

The introduction outlines the subject, purpose and scope of the report. It
may contain background information regarding the topic.

Scope and nature of the profession

This section contains a description of the nature and range of past and
current work carried out by the person that you have chosen in the
telecommunications engineering industry. It outlines the typical tasks
carried out by this engineer or technical person.

Training for the profession

This section outlines the training that this person has undertaken to work
in their chosen sector of the telecommunications profession. This section
should also define and examine the skills required for this area of the
profession.

Current projects, innovations and technologies in this profession

This section examines current and emerging projects that the individual is
involved with in their role in the profession. Where possible, this section
describes the situation that led to the development of the projects.

This section also describes any current or unique technologies used by

this person that are associated with or unique to this profession.

Management practices in the telecommunications industry

This section outlines the management tasks and responsibilities

associated with this persons role in the industry.

Health and safety issues

This section examines any health and safety issues that the person has to
deal with in the telecommunications industry. These may be associated
with the design, development, manufacture and implementation of
projects or with the processes that they deal with in their daily work.
This section should then explain how these issues are dealt with in the
industry.

Conclusion

This section draws to conclusion the elements outlined and developed in

the preceding sections. It should summarise any major points or issues
that have been detailed in the preceding sections.

Telecommunications engineering scope of the profession 32

 Acknowledgements

The acknowledgement section provides the opportunity to credit the work

or assistance of other people who contribute to the report.

References

To demonstrate that the report is well researched this section should

include all references. The Harvard standard referencing system should
be used. For example,

Higgins, R.A. 1977, Properties of Engineering Materials, Edward

Arnold, Sydney.

Appendices

Contains information separated from the main body of the report. The
information may include drawings, diagrams, photographs and tables that
may enhance the information presented in the main body of the report.

Sample report
The engineer who was interviewed for the sample report is a senior
engineer for a very large multinational telecommunications company.
This engineer has extensive experience in developing leading edge
technology. In compiling your engineering report you are not expected
to find a person with this level of experience. Moreover, you are
expected to interview people that are readily accessible from your
location.

The name of the engineer has been changed to protect their privacy.

Part 1: Scope of the profession and engineering report 33

Telecommunications engineering scope of the profession 34
Telecommunications engineering

Title Page

Title: The human face of telecommunications engineering

Module: Telecommunications engineering

Author: Anna Log

Date: August 2001

Abstract
This report examines the scope and nature of the work carried out by
an electrical engineer, Nikki Tesla, working for a large multinational
telecommunications company, Alcatel. Aspects of the engineers role
including past and present projects, management issues, professional
development, current technologies and health and safety issues are
discussed and analysed.

Introduction
Nikki Tesla is an engineering and technical manager with the
Australian division of a large telecommunications manufacturing
company called Alcatel. Similar multinational telephone companies
include Ericcson, AT&T and Seimens.

Nikki has been a practising engineer for approximately 20 years with

experience in hardware and software design of telecommunications
systems. Nikki worked briefly for another company which designed
thermocouples and temperature control equipment.

Training for the profession

Nikki had an early interest in electronics. She designed and
constructed many electronics projects while still at school. Her initial
engineering training was a Bachelor of Electrical Engineering from the
University of NSW. She graduated in 1980. Her major undergraduate
project was to design a computerised engine management and ignition
control system.
 As with all new engineers and staff at Alcatel, Nikki was given
training in the companys ethos and in the specialist areas relating to
her work. For example, when she first joined Alcatel, Nikki completed
an in-house, one week basic electronics soldering course. As a senior
engineer Nikki is currently completing an international advanced
management course. This requires her to attend two week training
sessions in Paris every two months (its tough but someone has to do
it).

Alcatel is involved in installing and upgrading hardware and software

connected to Australias telephone network and this often involves
real-time programming.

Real-time programming requires the engineer to make software

upgrades and changes on a software program that is actually running
and controlling active telephone exchanges. In this situation a small
error could result in a whole town or major sections of a city being
without a phone network.

Alcatel provides comprehensive training for new staff in techniques

for real time programming and training in the precautions that need to
be taken when doing real time programming. From a legal and ethical
view-point the company is directly accountable for any downtime it
causes this is especially so with the 000 emergency services.

Scope and nature of the profession

Alcatel has been involved in a wide and varied range of
telecommunications activities including telephone design, telephone
exchange design and manufacture, manufacturing undersea optical
fibre cables, mobile telephone technology provision, microwave
transmission equipment and communication technology for satellites.

Nikki has been primarily involved with telephone exchanges and

transmission systems since joining Alcatel. The past 20 years with this
company has seen a revolution in the equipment it designs, installs and
maintains.

When Nikki first joined Alcatel, exchanges were large, noisy electro-
mechanical systems based on the principles developed nearly 90 years
before by people such as Strowger. Now, all Australian exchanges are
fully digital and systems such as ADSL and 3G mobile are ready to be
trialled and implemented.
Current projects, innovations and unique
technologies
In the early 1980s, Telecom Australia decided to convert the
Australian telephone system from analogue exchanges to fully digital
exchanges. Soon after, Nikki became involved in the hardware and
software design of the System 12 digital telephone exchange. This is
one of the current exchanges used on the Australian telephone network
and represents the current technology in telephony. Through her
involvement in the System 12 project Nikki spent several years in
Belgium and Austria working with Alcatels European branches. The
overall project took approximately 15 years.

A recent project that Nikki has had input into was the automation of
directory assistance for Telstra. This is where advanced voice
recognition software is used to automatically recognise the names of
commonly called companies and then automatically tell the subscriber
the phone number requested. For instance, if you call directory
assistance wanting to know the number for QANTAS, a computer will
ask for the name of the company you need. Providing it can
understand you, the computer then reads out the number requested or
offers to connect you directly to that company.

Nikki has also been involved in developing Voice over IP

communications ability for hardware supplied by her company.
Associated with this Nikki has seen some of the development work
being done on 3G telephony at present and may move into this area as
it comes on-line.

Nikki sometimes uses computerised management tools and technology

to help organise her tasks. The management software QSM for
instance, can use critical parameters such as resource profiles, size,
lead-time and largest / smallest work component to help predict
scenarios and completion times. Spreadsheets such as MS Excel are
also used for planning tasks.

Management practices in the telecommunications

industry
As a technical manager Nikki is responsible for a large team of
engineers, software analysts and technicians. The training for these
professionals is available at most of Australias major universities. She
is also legally responsible for monitoring the occupational health and
safety of the team. Nikki divides her management responsibilities into
three areas:
 Functional management ensuring the infrastructure and
performance of the department is sound. This includes oversight of the
budget and purchase of equipment, recruiting and selection of staff,
professional development and supervision of staff on her team and
maintaining morale. One point that was made by Nikki was that team
morale was high when there was a modest level of work overload.
That is, people didnt enjoy having too little to do.

Management of the quality of work this includes monitoring

and correcting the level of defects in the final product be it software or
hardware, determining and setting the metrics for each project (the
constraints and limiting factors), system level testing, acceptance
testing for new installations, determining the teams level of
compliance with quality standards such as ISO 9000 and monitoring
the level of coding errors in software, (errors per 1000 lines of code).

Occupational health and safety The team is concerned with

software design and does not do any manufacturing. As a
consequence the occupational health and safety issues are fairly easily
identified and dealt with. Team members are regularly given the
opportunity for OH&S training but this training is often directed
toward safety issues in industrial and manufacturing settings. Machine
guarding, chemical risk assessment and use of PPE is emphasised but
the workers do not use this type of equipment.

Health and safety issues

The work environment of the software developer is somewhat
cloistered. The primary OH&S issues are concerned with adequate
lighting, ergonomic furniture, radiation and glare from VDU screens
and ensuring that the cabling and leads for computers are arranged so
as to prevent a trip hazard.

In this office the occupational health and safety issues are more
mundane and include :

providing ergonomic furniture for staff operating computers

staff being aware of correct lifting techniques eg for carrying

boxes

VDU units adjusted to the correct heights and glare reduction

incorporated

computer cabling and other trip hazards eliminated by careful

office planning

lighting , temperature and noise maintained at comfortable levels

 staff aware of emergency evacuation procedures

Staff are also given information on correct lifting and carrying

techniques.

Conclusion
Nikki has followed a typical career path for an electrical engineer. She
began as a hands on junior engineer with a sound knowledge of
electronics but with limited management skills. Nikki is now a
technical manager, supervising a large team of communications
specialists. Her skills base now includes her initial electronics as well
as advanced software design skills and industrial management skills.

It is conceivable that she will move into a senior management position

in the future or another role in the company such as sales or contract
negotiation.

In her time with Alcatel, Nikki has seen and been part of a major
revolution in telecommunications. Digital exchanges have replaced
analogue technology and the Internet has changed forever the way in
which people view and use their telephones.

Acknowledgements
I would like to thank Nikki Tesla from Alcatel and Con Ductor from
the UNSW for their assistance in preparing this report.

References
Higgins, R.A. 1977, Properties of Engineering Materials, Edward
Arnold, Sydney.

Murray, J. 1995, Calling the world. The first hundred years of Alcatel
in Australia, Focus Publishing, Double Bay.

Appendix
40 Telecommunications
 Exercise

Exercise 1.1

Interview an engineer or technician currently employed in the

telecommunication industry and report on the following aspects of the
interviewees professional employment.
Training undertaken to practice and gain promotion in the industry.
The nature and scope of the work carried out.
Current projects, innovations and unique technologies used in day to
day work and any emerging technologies that may affect future work.
Management practices used by the interviewee or employer.
Health and safety practices and issues associated with day to day
work.

Present your report following the structure of the sample engineering

report.

Part 1: Scope of the profession and engineering report 41

42 Telecommunications
 Progress check

During this part you examined the scope of the telecommunications

profession and explored current and emerging technologies in the industry.
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.

Agree well done

Uncertain
Disagree

Disagree revise your work

Agree

Uncertain contact your teacher

I have learnt about:

nature and scope of telecommunications engineering

health and safety issues
training for the profession
career prospects
relations with the community
technologies unique to the profession
legal and ethical implications
engineers as managers
current applications and innovations.

I have learnt to:

define the responsibilities of the telecommunications

engineer
describe the nature and range of work done in the
profession
examine projects and innovations in the
telecommunications profession
analyse the training and career prospects within
telecommunications engineering.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

During the next part of the module you will trace the history of
telecommunications.

Part 1: Scope of the profession and engineering report 43

44 Telecommunications
 Exercise cover sheet

Exercise 1.1 Name: _____________________________

Check!
Have you have completed the following exercise?
Exercise 1.1

Locate and complete any outstanding exercises then attach your

responses to this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your
responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learners Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.

Part 1: Scope of the profession and engineering report 45

Telecommunications engineering

Part 2: Telecommunications engineering

history of telecommunications
 helvetica helvetica

Part 2 contents

Introduction ..........................................................................................2

What will you learn?...................................................................2

History of telecommunication............................................................3

Harnessing electricity .................................................................7

The telegraph .......................................................................... 10

The telephone ......................................................................... 15

Wireless.................................................................................. 25

Television................................................................................ 29

Digital telecommunication......................................................... 30

The World Wide Web ............................................................... 33

Societal influences................................................................... 34

Exercises............................................................................................37

Progress check .................................................................................43

Exercise cover sheet........................................................................45

Part 2: Telecommunications engineering history of telecommunications 1

 Introduction

Effective communication is one of the most taken for granted forms of

modern technology. We simply expect our radios, television receivers,
telephones and computers to work. If they do not work it is no longer difficult
to replace them, often less difficult and even less expensive than repairing
them. The change in lifestyle created by modern telecommunications and
consumerism has significant implications for the responsible use and disposal
of natural resources as well as issues of privacy and ethics.

As you investigate the development and use of telecommunication

systems you should keep in mind the following questions:
Did a change in materials and an understanding of physical sciences
lead to a change in design?
Was a new and innovative design developed using existing materials
and knowledge?
What was the influence of new construction and processing methods?
In what ways did developments in related technologies influence
change in telecommunications?
How have these changes impacted on society and the environment?

What will you learn?

You will learn about:
historical developments in telecommunications
the effects of innovations in telecommunication on peoples lives and living
standards
environmental implications of telecommunication systems.
You will learn to:
research the history of telecommunication in Australia and
understand the way it has impacted on peoples lives
examine safety issues related to the use of telecommunication
systems.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

2 Telecommunications engineering
 helvetica helvetica

History of telecommunications

All communication was once by word of mouth and picture writing. As

the world population increased and people became more mobile it was
necessary to improve communication. The gradual changes from
isolated tribe to scattered village centres and then to major international
cities created two needs better communication and consequently better
literacy.

Early forms of communication required the sender to know the position

of the receiver. Messengers on foot or horseback were vital to early
communication networks. Where some form of semaphore was used
then either the sender and receiver had to be in line of sight with each
other, or some form of repeating station had to be created. It was not
uncommon for the message to be changed in some way as it was
transferred through these repeating stations, the person responsible for
relaying the message either misunderstanding or misinterpreting the
content of the message. Sending messages at night or in bad weather
created even more difficulties. Where animals were used to relay written
messages it was never quite clear whether a lost message was due to poor
training, natural enemies of the animal, or the animal being intercepted
by unknown people. These forms of communication were often
unreliable and, by the standards we now take for granted, very slow.
Messages could take weeks to be delivered.

Modern telecommunication relies on the ability to use and control

electricity. Consequently telecommunication was revolutionized with
early developments in the understanding and use of electricity.
Subsequent telecommunication evolution was achieved when the ability
to manipulate electricity was extended. The development and use of
electrostatics for transmission by modulated airwaves provided the final
revolution for the creation of telecommunication systems as we know
them today, linked by invisible wireless waves across the earth and
beyond.

The earliest forms of telecommunication by electricity relied on hand

operated electrical switching machines such as Morse code senders.
With no electrical amplification available, these systems continued to
require repeater stations and the security of the electrical wires needed

Part 2: Telecommunications engineering history of telecommunications 3

 to conduct the electricity was difficult to maintain through isolated areas.
The use of undersea telecommunication cables to link continents created
many practical difficulties that could not be solved until 1866 when the
first successful trans Atlantic cable was laid. The age of international
telecommunications had begun. Although these early forms of
telecommunication suffered some of the disadvantages of the
communication systems they replaced, they did have other great
advantages particularly their ability to deliver messages very much
more quickly and over greater distances than any previous forms of
communication.

As you read through this section you will discover the link between
telecommunications and developments in the knowledge and use of
electricity and electronics.

To provide a framework and a summary around which to build on your

knowledge, read through the following time line.

4 Telecommunications engineering
 helvetica helvetica

1200 BC Homer in his work The Illiad, 1861 America is connected coast to
discusses signal fire being used coast by the electric telegraph.
for communication. 1865 The first Atlantic telegraph cable
700 BC to 300 AD Carrier pigeons was laid.
used by the Greeks in 1873 Heinrich Hertz confirms the
association with the Olympic existence of electromagnetic
games. waves.
600 BC Thales of Miletus is reputed to 1874 Thomas Edison invents
have rubbed amber on cat fur multiplex telegraphy.
to produce static electricity.
1876 Alexander Graham Bell patents
1600 AD William Gilbert wrote about the first telephone.
magnets and magnetic effects.
He proved that attraction due 1877 Western Union has the first
to static electricity was not a telephone line in operation
magnetic effect. between Boston and
Sommerville.
1675 Robert Boyle realized that
electrostatic force could be 1880 American Bell Telephone
transmitted through a vacuum. Company is founded. There are
30 000 phones in use.
1729 Stephen Gray distinguishes
between conductors and non- 1882 Bell obtains a controlling interest
conductors (insulators). in Western Electric, a former
telegraph company. This
1746 Benjamin Franklin concludes company had earlier rejected
that electricity is a fluid. Another Bells offer to sell them his
scientist Henry Cavendish, telephone patent.
experimenting with current,
includes himself in the circuit to 1891 A. B. Strowger, an undertaker,
estimate current flow. invented the automatic dial
system for telephones to
1786 Luigi Galvani noticed the effect eliminate the operator from the
on a frogs leg when electricity system.
was discharged through it.
Later, Alessandro Volta invents 1895 Marconi demonstrates voice
the battery. radio transmission.
1793 The Chappe brothers, two 1897 Thomson discovered the
young Frenchmen, established electron, adding significantly to
the first commercial semaphore the understanding of electricity.
signaling system near Paris. 1904 John Fleming invents the
The signaling rate was about vacuum tube.
15 characters per minute. The
1907 Lee De Forest added a third
semaphores use spread across
electrode to the diode and
Europe and to parts of the USA
created the first electronic
and employed thousands of
amplifier, the triode.
workers over a 40 to 50 year
period. 1913 Robert Milikan measured the
charge on a single electron.
1827 G.S. Ohm discovers the
relationship between voltage, 1910 Peter De Bye, a Dutchman,
current and restistance develops a theory about optical
V = I x R. wave guides. The practical
application of this theory is
1837 Charles Wheatstone patents an
optical fibre. It was many more
electric telegraph.
years before it became possible
1844 Samuel Morse further develops to produce this as a viable
and demonstrates the electric product.
telegraph.
1915 Valve amplifiers are first used
1851 51 telegraph companies are in in coast to coast telephone
operation. circuits.

Part 2: Telecommunications engineering history of telecommunications 5

 1926 Baird demonstrates an electro- 1970 Intel releases the 4004
mechanical TV using spinning microprocessor chip. The chip
discs and neon bulbs. The idea is only a 4 bit processor but
worked but a more versatile and improvements in its design led
wholly electronic system was to the 8086, 80286, 80386 and
soon to follow. 80486 series of chips.
1928 Zworykin patents files for an 1971 Xerox patents the first laser
electronic scanning television printer.
system. 1974 The first domestic ( non-military)
1935 The first telephone call made satellites launched. The concept
around the world. of an Internet is proposed by
1937 Bell Telephone Labs (BTL) Vint Cerf and Bob Khan.
introduces the Model 300 1975 The use of optical fibres for
telephone handset telecommunications is trialed in
1939 John Atanasoff and Clifford the USA. The 5.25 floppy disk
Berry of Iowa State University drive was produced by Alan
invent the first electronic Shugart at IBM.
computer. 1976 ISD (International Subscriber
1947 BTL introduces a germanium Dialing) introduced in Australia,
point contact transistor. This is allowing direct dialing to 13
the beginning of the solid state countries.
era and the decline of the use 1979 Visicalc , the first computerised
of vacuum tube technology. spreadsheet was invented by
1954 Sony releases the first transistor Dan Brinklin. Dan is still at
radio. college at that time.

1955 A.W. Morten and H.E. Vaughan 1981 IBM releases the IBM PC
release a paper called The (Personal Computer) computer
Transmission of Digital and thus begins the 80xxx and
Information over Telephone Pentium series of computers
Circuits. They were in fact that we are so familiar with
describing the first real modem. today.
IBM develops the first disk drive. 1987 Sony releases the first 3.5
1957 Sputnik-1 was launched by the floppy drive and IBM introduce
Russians. It is the first satellite. the first hard drive suitable for
use in an IBM PC. It held a
1958 A big year Texas Instruments maximum of 10Mbytes.
create the first integrated circuit
and introduce the first silicon 1992 Tim Bernes-Lee a physicist,
transistor. These two develops the World Wide Web
developments form the basis of (WWW).
modern solid state electronics. 1993 The MOSAIC internet browser
Seymour Cray produces the is introduced, the Netscape
first computer to ultilise browser comes on line the next
transistor technology. year, 1994.
1964 The concept of a mouse is 1996 A 56 kbps modem chipset
patented by Douglas Englebart announced by Rockwell.
at Stanford Research Institute However most phone lines are
( SRI) and George Heilmeier capable of only 42 to 44 kbps
invents the liquid crystal display using this technology.
( LCD). 1997 ISDN lines capable of 128 kbps
1969 The US Department of Defense are announced.
initiates the ARPANet program 1998 The modem standard V.90 56K
which eventually leads to the was approved.
development of the present day
Internet. It is initially only for
military and academic purposes.

Now you have an overview, lets go through it in a little more detail.

6 Telecommunications engineering
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Harnessing electricity
The effects of electricity were first noticed in natural occurrences. The
attraction between amber stone that had been rubbed with cat fur and
small bits of straw was noticed by the Greek philosopher Thales around
600BC. Another Greek philosopher, Plato, made a similar observation
around 300BC. Almost 2000 years later in 1551 an Italian
mathematician, Jerome Cardan, examined the attraction between
loadstone and iron and compared these observations with similar
occurrences around amber. By 1600 William Gilbert, an English
physician, had noticed similar properties in diamond, glass, sulfur and
wax. Gilbert classified these materials as electrics from the Latin word
electrum for amber. The English physician Sir Thomas Browne first
used the term electricity in 1646.

Wow! weve just covered 2200 years in a paragraph. However, things

were starting to hot up. Lets continue....

With continued investigation into electricity various discoveries

followed. In 1729 Stephen Gray, an English scientist, found that some
materials were electrical conductors, and others were not. Charles Du
Fay, a French scientist, found that some objects repelled each other,
while others showed attraction. In 1746 Benjamin Franklin, an American
inventor, scientist and diplomat, concluded that electricity was a fluid
and positive objects had an excess of this fluid while negative objects had
less of this fluid than they required. Franklin proved that lightning is
electricity. His theory explained the attraction between oppositely
charged objects, repulsion between like charged objects and the
neutralizing of charge when this fluid could flow between oppositely
charged objects after they come into contact. Later work by other
scientists would refine these concepts, introducing the electron and
determining that Franklins positive objects actually had a deficiency of
electrons while his negative objects had an excess of electrons. In 1785
Coulomb, a French physicist, formulated the laws of attraction and
repulsion between charged bodies.

How would you explain the attraction and then the neutralising of charge
using a flow between oppositely charged objects?
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________

Part 2: Telecommunications engineering history of telecommunications 7

 Did you answer?

A negatively charged object has an excess of electrons. A positively charged

object has a shortage of electrons. These objects will attract each other because
they have opposite charges.

If they touch, the electrons can flow (move) from one to the other. If there are
enough electrons, the positively charged object can be neutralised by replacing
its missing electrons.

In 1786 the first observations that were to lead to the invention of the
battery were made. A freshly killed frog was made to twitch. It was
supported on a copper hook and brought into contact with an iron railing.
A flow of electricity through the body of the frog resulted from the
reaction between the dissimilar metals that were electrically connected
by the still moist frog. This observation was wrongly thought to have
indicated that the frog contained animal electricity. Some 15 years
later, in the late 1790s, Count Allessandro Volta, an Italian physics
professor, discovered that two different metals connected by a
conducting liquid could produce electricity. He built the voltaic pile
the first battery. His battery consisted of a stack of silver and zinc discs
in pairs separated by a sheet of paper that had been soaked in salt
solution. This invention was the first source of steady electric current.
Without this discovery, the laws of electricity could not have been
derived and modern telecommunications systems would not have been
developed.

About 20 years later, in 1820, Hans Oersted, a Danish physicist, noted

that a strong current passing through a wire would move the needle of a
compass held near it. The magnetic field around a flowing current had
been discovered, and electromagnetism was born. The French physicist
Andr Ampre then immediately formulated detailed laws concerning the
forces of attraction and repulsion between current-carrying wires. By
1831 Michael Faraday, an English physicist, and Joseph Henry, an
American physicist, had separately reasoned that if a moving current
could produce magnetism, then moving magnetism could produce a
current. The invention of electric generators and transformers followed.

8 Telecommunications engineering
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An early capacitor An early battery Generator

Figure 2.1 Early developments in electricity

World Book Encyclopaedia, 1985, Vol.6, p.152

The concept that electricity could produce electromagnetic waves that

would travel without a conductor at the speed of light was first suggested
in equations for the laws of electricity and magnetism formulated by
James Maxwell, a Scottish scientist, in 1873. In the late 1880s Heinrich
Hertz, a German physicist, produced these waves.

Consider some of the advantages of sending wireless messages (using

electromagnetic waves).

___________________________________________________________

___________________________________________________________

Did you answer?

messages can be sent reliably any time of the day

no cables needed to be installed
no cables to be damaged and maintained
messages can be sent over inaccessible terrain
messages can be sent to any location in wireless range

The existence of the electron, and its function in the flow of electricity,
was suggested by Stoney, an Irish physicist, in 1891. By 1897 Joseph
Thompson, an English physicist, had confirmed this theory and further
discovered that all atoms contained electrons. In 1913 Robert Millikan,
an American physicist, was able to measure the exact charge on an
electron.

Electronics began when John Fleming, an English scientist, built the first
vacuum tube or valve in 1904. These devices were tubes containing very

Part 2: Telecommunications engineering history of telecommunications 9

 little air, a near perfect vacuum, through which electrons could be made
to flow in a controlled way. Flemings vacuum tube could detect radio
waves, a type of electromagnetic wave. In 1907 Lee De Forest, an
American inventor, produced a vacuum tube that would amplify, that is
make stronger, radio waves or signals. Radio as we know it was made
possible by these vacuum tubes. Vacuum tubes also led to the
development of television and radar between the 1920s and 1930s and by
the 1940s electronic computers had become a reality. The large size,
unreliability, current demands and sensitivity of valves to heat and
vibration led to the development of the transistor in 1947 by three
American physicists Barden, Brattain and Shockley. Continuing
development saw the integration of whole transistor circuits into single
devices called integrated circuits by the early 1960s. In less than 20
years the transistor and associated semiconductor devices totally
replaced valves in virtually all electronics industries. Continuing
miniaturisation and other developments led to the microprocessor and
personal computer. All electronic equipment continues to become
smaller, more reliable, less costly and more useful as this development
proceeds.

Triode (1907) Transistor (1947) Integrated circuit (1960s)

Figure 2.2 Developments in electronics (note the miniaturisation with time)

Source: World Book Encyclopaedia, 1985, Vol.6, p.153

The telegraph
Telegraphic or distant writing (from Greek words) communication was
the first form of messaging to use electricity. It was the dominant form
of communication for over 100 years. At one stage the telephone was
expected to replace the extensive telegraph infrastructure stretching
around the world but this proved to be only partly correct. It was not
until the development of the personal computer and the creation of the
Internet that communication by telegraphy finally became outdated.

10 Telecommunications engineering
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Why was the telegraph unable to compete with the Internet?

___________________________________________________________
___________________________________________________________
___________________________________________________________

Did you answer?

The telegraph requires operators and specialist terminals or some other delivery
system. This uses time and money resources. People are able to complete these
tasks for themselves on an Internetlinked computer terminal. The Internet
offers the computer owner a method of sending and receiving messages exactly
when required and enables the immediate posting and receiving of linked
documents. All of this involves little additional cost over that of a computer
that has usually been purchased for other tasks such as word processing.

Cooke and Wheatstone in England and Morse and Vail in the United
States invented the telegraph simultaneously. Earlier work by Oersted
and Volta and the invention of the electromagnet in 1825 by William
Sturgeon (a British electrician) were combined to make the first
messaging by telegraph a reality.

The English telegraph used six wires to provide electrical energy to five
needle pointers. Depending on the signal sent through the wires letters of
the alphabet were pointed out by the needles. In this way a message
could be received and assembled letter by letter. This system was used to
improve efficiency and safety between railway stations in London around
1837.

Likewise the telegraph invented by Morse and Vail in the United States
used a punching system to show the transmitted message, in this case on
a soft tape. The first public use of this system was between Washington
and Baltimore in 1844. With use it quickly became apparent that the
sound of the equipment being used to record the letter characters
provided a much faster method for the operators to receive a message.
By 1856 telegraph messages were received by sound recognition from
redesigned sounding equipment. This replaced the registers first used to
make a record of the message that could be seen.

Just before WWII, an American submarine, the Squalus, transmitted its

position using Morse code just before it commenced a practice
emergency dive. Unfortunately, an air inductor valve did not fully close
and the submarine partially flooded leaving 33 of the crew trapped on the
bottom. In addition the assumed position of the submarine was out by
more than 5 miles because one digit in the position was incorrectly
transcribed during the Morse transmission. Fortunately a rescue vessel

Part 2: Telecommunications engineering history of telecommunications 11

 discovered the submarines true position by accident and the surviving
crew were rescued.

Use your library or the Internet to find the Morse code. Then write the
morse code symbols for the word MORSE in the space below.

Did you answer?

.. ... .

The Morse telegraph using sound generated by closing metal contact

points was simple and reliable, and became the preferred system.
However, the code of dots and dashes originally developed by Morse for
his telegraph proved unsuitable for languages other than English and so
was replaced by International Morse Code in 1851. The dots and dashes
that characterise telegraph codes soon proved impossible to transmit
reliably over long distances through undersea cables. Without the
technology to provide undersea repeater or amplifier stations the dots and
dashes became distorted due to the electrical capacitance of very long
cables. The solution to this problem was found in sending positive and
negative impulses along the cable instead of dots and dashes. This
development also provided the basis for later radio codes that would
allow the transmission of more messages more quickly and
simultaneously.

Figure 2.3 The main telegraphs receiving room at Darwin

Jensen. P. R, 2000, p.8

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The first telegraph sending and receiving instruments could transmit one
message at a time. In 1871 an American by the name of J. B. Stearnes
developed a duplex transmission that allowed sending and receiving to
occur simultaneously. This doubled the capacity of the telegraph lines.

Figure 2.4 Morse key and sounder, c1870

Jensen. P. R, 2000, p4

The concept of time-division multiplexing, allowing even more

transmissions to be operated along a single line, was first introduced by
mile Baudot in France in 1871. He was able to create a system for
transmitting five messages simultaneously. Later technology would see
variations of the code he developed which would be used well into the
20th century in binary technology.

With the continuing development of the vacuum tube concept from 1904
came the next great improvement to the capacity of telegraph lines. In
1918 modulated carriers were used to pass messages along telegraph
lines. By varying the frequency of these carriers, and having senders
and receivers operating at selected carrier frequencies, it became possible
to send, receive and separate many messages simultaneously. With each
message being conveyed in a separate frequency band, the number of
simultaneous messages was only restricted by the frequency bandwidth
of each carrier and the limits of frequency transmission. In 1918 it was
possible to separate, or multiplex, 24 separate signals simultaneously.
Other improvements created by the vacuum tube included the electrical
amplification of weak signals to allow more reliable message
transmission over far greater distances. Improvements in magnetic
materials increased transmission speeds and permitted duplex operation
in very long submarine cables by 1928. Despite these improvements the
first successful underwater vacuum tube repeater was not possible until
1950. Just 15 years later valve technology became obsolete.

Turn to the exercise section and complete exercise 2.1.

Part 2: Telecommunications engineering history of telecommunications 13

 List as many advantages as you can for multiplexing information.
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

Less development of infrastructure required

Reduced maintenance of infrastructure
More efficient use of an existing resource
Greater availability of telecommunication facility to more people
Reduced user costs

Business requirements led to the introduction of teletype in 1924.

Messages were sent and received immediately in printed form removing
the need for a code operator. A special typewriter was used, greatly
reducing the time needed to convert a message into and from its electrical
form for the telegraph. At first, the five bit Baudot Code was adequate to
operate this system but as transmission and hardware speeds increased
with the introduction of computers, code limitations became the slowest
part of messaging. In 1966 a seven bit transmission code was established
and called the American Standard Code for Information Interchange, or
simply ASCII code. Code speeds of 150 words per minute replaced the
maximum 75 words per minute that had been possible using the Baudot
Code.

Telex, a switched teleprinter network, was introduced in 1932 and

operated manually until after World War II. This system was devised to
create the fastest possible messaging of news and commerce using
electro-mechanical devices.

The facsimile telegraph was perfected in the 1930s for transmitting

graphic information such as photographs by analogue transmission.
With the advent of digital transmission, which has now virtually
replaced analogue transmission, the digitally operating fax machine
evolved from facsimile telegraphs.

Today the telegraph, which started in 1837, has been replaced by digital
data transmission systems based on computer technology. New
electronics technology including transistors, integrated circuits now
containing thousands of components, and other micro electronic
inventions, have revolutionized the transmission of information and led
to the virtual universal adoption of digital communication. During this
time there have been profound changes in society and commerce.

14 Telecommunications engineering
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Efficient supervision by fast long distance telegraphy has led to the

replacement of many small separate businesses with large corporate
organizations, ultimately resulting in the development of multi-national
corporations. Public transport has been able to increase both in
complexity and safety due to the ability to rapidly and accurately locate
traveling trains and aeroplanes. At community level, people who have
moved for work or who are traveling for pleasure, are easily able to keep
in contact with family and friends, and so are more likely to move and
travel. As these trends have developed, businesses have banded together
to make the most efficient use of telecommunication systems.
Associated Press was formed in 1848 by six New York newspapers and
in 1849 Paul Julius Reuters established a telegraphic press service that
used pigeons to cover areas not linked by telegraph line. The rapid
distribution of news and information has changed the way people view
and react to events in other parts of the world.

Turn to the Exercise section and complete exercises 2.2 and 2.3.

The telephone
Telephones allow people to talk with one another even though they may
be a long way apart. The telephone developed with the telegraph.
Alexander Graham Bell, a Scottish born American inventor, applied for a
patent for his telephone on February 14, 1876. Only 2 hours later
another inventor, Elisha Grey, applied for a patent for a telephone based
on very similar principles. Bells patent, No 174-465, was issued on
March 7, 1876 and was the subject of many unsuccessful legal
challenges. It is probably one of the most valuable patents ever issued.

In the above paragraph you have read about patents. Outline what a
patent is and discuss why it is of such importance to inventors and
innovators such as Bell.
___________________________________________________________
___________________________________________________________
___________________________________________________________

Did you answer?

A patent is designed to protect the intellectual property of inventors. A patent
prevents other people/companies from manufacturing a product that you have
invented or developed. They are important because they allow you to make
some money from your inventions.

Part 2: Telecommunications engineering history of telecommunications 15

 Compared to the telegraph, the advantages of the telephone included its
ability to allow quick response in conversation and to convey some
feeling through the sound of someones voice. Unlike the telegraph,
the telephone did require people to be in a certain place at a certain time.
This, of course, is no longer the case. Today telephones can be totally
mobile and may even transmit written words, drawings, photographs,
video images and large amounts of data through connection to computer
terminals.

The original Bell telephones were sold in pairs and were directly
connected together much like an intercom. This was fairly limiting.
Soon, numbers of telephones were being connected together between
local residences and businesses. To simplify this network, telephone
exchanges were built so that a user, linked to the exchange could be
connected to any business or other user that was also linked to the
exchange. People were employed at the exchange to physically select the
desired lines. Melbourne had the first Australian manual exchange in
August 1880 followed by Brisbane two months later and Sydney in 1881.
It is interesting to note that the last manual exchange in NSW was at
Wanaaring. It was closed in 1991.

In 1891 a Kansas undertaker, AB Strowger patented an automatic dialing

and exchange system. You might wonder why an undertaker might
undertake such a task! The story goes that the wife or girlfriend of a rival
undertaker was employed at the local telephone exchange. Remarkably,
the rival undertaker suddenly started to receive many of the business
calls that Strowger should have received. Strowger then set about
designing a system that cut out the need for a manual exchange.

16 Telecommunications engineering
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Figure 2.5 A manual telephone exchange from the 1880s

Soden et al, 1996, p28

Being an undertaker, Strowger was a formal dresser: black suits, top-hats

and stiffened collars. The box that the stiff collars were purchased and
stored in was a rigid cylinder. Strowger was to use this as the basic
element of his automatic telephone switching system.

The Strowger system was the first example of step by step switching.
His prototype as described here could select 100 subscriber lines. To dial
the number 48, a user would push the first button on the dialer four
times. This was the first step and it moved the selector to the fourth
row. The user then pushed the second button eight times. This was the
second step. This then selected the eighth contact on that row and
directly connected the user to the desired number. To increase the
number of lines to one thousand the size of the cylinder was considerably
increased to allow the rows to be arranged in 10 groups of 10.

While many refinements were made to his system over the next 60 to 80
years, Strowger pioneered step by step switching and the concept of
pulse type dialing. His system was also the first automatic circuit
switching system, where phones are physically (electrically) connected
together without the need for operators. In 1993,in Australia, there were
still 188 000 lines connected to step by step type exchanges but they
were soon to be replaced by fully digital exchanges.

Part 2: Telecommunications engineering history of telecommunications 17

 Primary Secondary Subscriber
selector selectors lines

Callers phone Called

telephone
rings

Figure 2.6 The principle of a Strowger switching system

For the next forty years automatic exchanges based on Strowgers

original principles competed with large manual exchanges. Manual
exchanges remained popular for a number of reasons. They offered a
more personalized service, their initial installation costs were lower and
the operators were mostly women - the wages for women were about half
that of men in those times.

Women continued to be paid less for the same work until relatively
recently. Find out when women were legally entitled to receive equal pay
and to vote in Australia. Write your answer in the space below
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

1894 Women allowed to vote in South Australia (First)
1902 NSW women given the vote
1908 Victoria (Last) very slow to give women the vote
1972 Equal pay for equal work was granted to women

Improvements in telephone networks have developed through the

introduction of many new products and technologies. Some of the
developments and the problems from which they arose, are outlined
below.

18 Telecommunications engineering
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Problem New product / technology

A loss of signal in non-insulated steel 1 Method of producing hard-drawn

or iron wires copper wire (a much better
conductor) which could support
itself between poles was
developed. (1877)
2 Insulated covering put over wires

Every person you want to call must be Exchanges were established so that
connected directly to your phone only one line was required to each
phone (Melbourne in 1880)

There was a loss of electrical signal A two wire system was introduced
and interference (1870s and 1880s) (both wires connected into the system)
due to the wire needed to complete (1881)
the circuit being a ground return
(connected through the earth)

Connections between phone lines had Automatic exchanges were developed

to be done manually to replace manual exchanges (1891)

Signals were very weak and only able Invention of the vacuum tube to
to be carried short distances amplify signals (1904)

Cross talk interference between Wires were twisted at set distances

parrallel conductors along a network. along the network. (reduced the effect
of electromagnetic induction)

A loss of signal over long distances Inductance coils were placed along
due to capacitance in long wires the telephone wires. (1904)

A large network of cables and poles 1 Cables were placed underground

was required and under the sea.
2 Optical fibres are replacing metal
cables. (from 1970s)
3 Radio and satellite transmission
was developed which doesnt
require cables

Only single conductor cables were laid 1 Carrier multiplexing ie multiple

over very long distances due to cost. messages were able to be
transmitted through single pair of
copper tubes in a coaxial cable
2 Fibre-optic cables were developed
requiring less amplification
(because less energy lost) and
were able to carry much more
information.

Part 2: Telecommunications engineering history of telecommunications 19

 Turn to the exercise section and complete exercise 2.4.

The telephone in Australia

In Australia, the first telephones appeared in Melbourne in 1878 and the
Melbourne Telephone Exchange Company was formed in August 1880.
In 1880 some Bell telephones were brought to Sydney and installed in
the warehouses and wharves of Darling Harbour (S.M.H. 7th August
1880). In 1887, the Victorian Government had taken over the Melbourne
Telephone Exchange Company and had 1462 subscribers by 1888.

Figure 2.7 A set of telephones displayed at the 1880 Sydney Exhibition

Soden et al 1996, p27

Trunk services between the capital cities took a little longer. The Sydney
to Melbourne trunk line was opened in 1907 and the Melbourne to
Adelaide trunk line was opened in 1914. The development of radio
communication enhanced the ability to make telephone calls over great
distances. In 1927 overseas beam radio was introduced and in 1930 an
Australia to United Kingdom radio link was established. Radio, while
covering great distances, had many technical problems that limited its
reliability and bandwidth.

The 1950s onwards was to see massive radical changes in the

transmission systems and bandwidth available. In 1953, Perth became
the first capital city to have a fully automatic telephone network. By
1957 nearly all telephones in capital cities were connected to automatic
exchanges.

20 Telecommunications engineering
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Laying cables to carry telecommunications signals is both time

consuming and costly. Microwave radio technology allows broadband,
high quality communications. In 1958 the first microwave trunk link
was established between Melbourne and Bendigo. This technology now
services thousands of kilometers of Australia. Microwave radio relies on
line of sight transmitting and receiving and therefore uses tall towers on
the top of the highest available terrain. You will often see these tall
towers with their round receiving dishes as you travel around both
metropolitan and rural Australia.

The COMPAC transpacific undersea cable was opened in 1962, bringing

a new era of reliability and quality to international telephone
communications compared to that offered by the older radio system.

Satellites are the ultimate microwave tower, offering direct line of sight
communications to any ground station below it. In 1966 the first satellite
broadcast between Australia and the United Kingdom occurred. By 1968
the Australian communications network was linked to the first global
satellite communications system. This was facilitated via an earth station
near Moree in northwest NSW.

In 1976 International Subscriber Dialing was introduced giving

Australians access to 13 countries. Previously the call would have been
manually connected.

Part 2: Telecommunications engineering history of telecommunications 21

 How a telephone works
A telephone handset consists of:
1 a dialing mechanism
2 a transmitter
3 a receiver.
So that people can contact a particular telephone on a network containing
millions of handsets it is necessary for each subscriber to have a particular
electrical address on the network. The dialing mechanism enables contact
with a particular subscriber. The first dial telephones were introduced in
1896. Prior to this press buttons or an operator were used to establish
telephone connections. The ringing signal to gain the attention of the operator
or receiver was first generated by the sender turning a crank on the sending
telephone.
At first dial telephones used a coded sequence of electrical pulses created on a
rotary dialing mechanism, or later a push button keypad, to establish electrical
connection with a particular telephone. We commonly refer to this coded
sequence as the telephone number.

Figure 2.8 A rotary dialing mechanism

Today all telephones use a keypad to create a coded sequence of tones that,
likewise, establish electrical connection with a particular telephone. The
transmitter is a microphone located within the handset. The carbon
transmitter was one of the earliest telephone transmitter designs and it
remained in common use until no more than thirty years ago. The carbon
transmitter produces a strong electrical output, very necessary before
electrical amplification could be easily produced. It is mechanically simple to
make and is very reliable. When speaking into a carbon microphone sound
waves cause a thin round aluminium diaphragm, to vibrate. The diaphragm
acts on a chamber containing many small grains of carbon. Electrical contacts
on either side of the carbon chamber allow a low voltage current to pass
through the carbon. When the grains of carbon are compressed by the
vibration of the aluminium diaphragm more current is able to pass through
them. With less compression, less current flows. In this way the sound
pressure waves from a voice are transformed into a varying electric current.

22 Telecommunications engineering
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carbon block
back contact front contact

to current source
button

diaphragm

Figure 2.9 Edisons carbon transmitter

Today, foil electret microphones are in use. They are much smaller than
carbon transmitters, more sensitive and able to reproduce a much greater
audio frequency range. Speech is clearer and the person more recognizable
through a foil electret microphone. The foil electret microphone consists of a
diaphragm and a backing plate. An electric field is established between the
diaphragm and the backing plate. Vibrations in the diaphragm change the
strength of this field during speech, and these changes in field strength are
used to create corresponding changes in an electric current for transmission
along the telephone line.

permanent
magnet
electro-
magnet

diaphragm

Figure 2.10 The receiver

The receiver consists of an iron diaphragm with a permanent magnet around
it. On the other side of the diaphragm an electro magnet receives a varying
electric signal from a distant telephone. This varying signal creates a varying
magnetic pull on the diaphragm from the electromagnet, and this varying
force in turn causes the diaphragm to vibrate in the same pattern as the electric
signal in the electromagnet. In this way a sound pattern very similar to the
pattern that produced the varying electrical signal in the transmitter, is
recreated in the receiver. Speech is then transferred from the sender to the
receiver.

Part 2: Telecommunications engineering history of telecommunications 23

 Modern developments in the telephone
As with the telegraph, modern developments in the telephone system
have relied on the creation of multiplexing systems to allow many
connections simultaneously on the one line, and also the use of radio
technology to assist long distance communication. Radio systems have
greatly expanded the number of subscribers able to use a single network.
Radio relay systems using microwaves to conduct signals along the line
of sight between relay stations are now extensively used. Satellites can
be used to carry many conversations simultaneously but, because of the
great distances involved in sending a signal to and from a satellite, a
noticeable delay is introduced between the speech of the sender and the
receiver. For this reason satellites are used for only one direction of a
two-way conversation, the other direction being transmitted by landline
or line of sight microwave link. Over the horizon radio relay systems
have also been developed, enabling the distance between relay stations to
be extended from 50 km to 320 km. This development reduces the
number of relay stations required along a line and enables the
transmission of signals across all but the very largest bodies of water
without the need to direct those signals to a satellite.

The cordless telephone and the mobile telephone also use radio signals to
remove the need for a physical connection, metal wire or glass fibre optic
cable, for at least part of the telephone network.

Figure 2.11 An early mobile telephone

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The first mobile telephones appeared in the 1930s, although these units
were more like mobile radios than mobile telephones. They were large
and heavy and could not be conveniently carried with the user.
Improvements in miniaturisation, most notably the development of semi
conductor devices and battery technology, allowed the transformation of
these units into the mobile telephones now in use. These changes have
greatly improved the convenience of the telephone.

The privatisation of Telstra in Australia has caused considerable debate.

List some concerns that illustrate the importance of the telephone to the
general community.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________

Did you answer?

removal of untimed local calls

userpays increases the cost for people in country areas
concern over maintenance standards
increase in charges generally, because of the need to produce a profit for
shareholders.

Now turn to the exercise section and complete exercises 2.5 to 2.7.

Wireless
In the early 1800s, work with electromagnets by Joseph Henry and
Michael Faraday indicated that a current traveling along one wire could
produce a current in another wire even though the wires were not
connected. James Clerk Maxwell explained this induction effect in
1864 as being the result of electromagnetic waves that traveled between
the wires at the speed of light some 300 000 km per second.

In the 1880s Heinrich Hertz proved the existence of these

electromagnetic waves, using a loop of wire to act as an antenna. Shortly
afterwards, experiments by Edward Hughes showed that a steel point
placed onto a carbon block would not conduct a current unless
electromagnetic waves traveled through the point of contact at the same
time. In a similar way, electromagnetic waves produced by a spark

Part 2: Telecommunications engineering history of telecommunications 25

 transmitter could be used to switch a distant current by creating an
attraction between zinc and silver filings in a glass test tube. The current
to be switched was supplied to the filings by a battery or voltaic cell as
batteries were then known. Sir Oliver Joseph Lodge used this discovery
to produce a coherer, a device which could detect the presence of radio
waves.

An improved coherer was needed to make better use of radio waves for
improved reception and in 1895 Gugliemo Marconi, an Italian electrical
engineer and inventor, achieved this. In 1897 he transmitted radio
signals 29km from land to a ship at sea. In 1899 he was able to send a
radio signal between England and France and by 1901 he achieved the
transmission of a single letter across the Atlantic Ocean between England
and Newfoundland.

There was some thought that wireless communication would only work
along a direct line of sight. In fact, due to the earths curvature, it was
believed by some scientists that wireless communication systems would
not be able to provide true long distance communication. This,
obviously, was proven to be incorrect. In fact, longer radio waves are
reflected by the ionosphere and literally bounce back to earth, thus
increasing their transmission distance around the earth.

ELEVATED WIRE ANTENNA

RF CHOKE BATTERY 1 BATTERY 2

TAPPER
METAL FILINGS

COHERER PAPER
TAPE
PRINTER
SENSITIVE RELAY
(NORMALLY OPEN)
RF CHOKE

EARTH

Figure 2.12 Marconi coherer receiver 1895

By 1905 radiotelegraphy between ship and shore was becoming more

common. The sinking of the Titanic in 1912 and the subsequent rescue
of hundreds of passengers was an early instance that would help establish
the necessity of radio telecommunication to a society that was becoming
more demanding in its expectations of modern technology.

26 Telecommunications engineering
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Despite these advances, the use of radio communication was limited to

signaling by code, and once again, it was only with the invention in 1907
of an electronic valve that could amplify radio signals that radio made its
first real advances towards the system that we know today. In 1906 one
of the first broadcasts of human speech was achieved between land and
nearby ships at sea from Massachusetts in the USA.

As with the telephone and telegraph, ongoing development of radio

telecommunications would be dependent on developments in electricity
and electronics. Valves were quickly improved to act as better detectors,
amplifiers and oscillators. Wireless, or radio telephony became useful
for sending long distance spoken messages as early as 1915 when voice
communication was established between Virginia in the USA and
Hawaii, and then Virginia and Paris in Europe.

In 1918 radio transmission became truly effective and its great potential
began to be fully realized with the development of the super heterodyne
circuit by the American inventor Edwin H Armstrong. This circuit
greatly increased selectivity and sensitivity in the reception of radio
waves. In 1933 the same inventor developed FM broadcasting in
response to community pressure for improved sound quality in
commercial broadcasting.
Drive motor High-v
oltage
bus
1
2
3
Spark gap 4

High-v
oltage Common shaft
bus

Figure 2.13

Part 2: Telecommunications engineering history of telecommunications 27

 DRIVE MOTOR
ANTENNA
DIRECT CURRENT
GENERATOR

SG SG

ALTERNATING 1
CURRENT
SOURCE

2 EARTH

Figure 2.14 Creating continuous Radio Frequency electromagnetic waves

from sparks in 1918

After World War I amateur radio operators did much to develop the use
and understanding of radio transmission. Transatlantic voice radio
contact was made in 1921 and valuable voluntary assistance was
regularly supplied in emergencies. Australias first commercial radio
station was 2SB which began AM broadcasts in Sydney in 1923. Just
two years later on Australia Day in 1925 2UE also began AM broadcasts
in Sydney.

Towards the end of the 1920s the super heterodyne radio receiver saw the
demise of the piano as the chief source of home entertainment, replaced
in most living rooms by the radio. Radio quickly became a medium for
conducting government propaganda during war times. It was used to
spread various political messages as well as providing true news and
entertainment.

As the methods used to create the radio frequency electromagnetic waves

improved, from irregular mechanical sparking systems to electrical
alternator methods and then to electronic methods, so the transmitter
became more efficient and more powerful. The widespread acceptance
of television from the 1950s was expected to end the radio era for
commercial broadcasting. The ability of the organisations using radio to
adjust to changing community wants such as news talk radio, other
special interest group radio stations and the spread of car radios has seen
radio transmission maintained as a dominant form of commercial
broadcasting.

28 Telecommunications engineering
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Although it has always been used for civil, military and commercial
communication, radio has only become a significant medium for data
transfer with miniaturisation and the development of digital computer
processing. Radio is now being connected to lap top computers to
improve their usefulness.

True intercontinental radio telecommunication became possible with the

development of the aerospace industry. Amateur satellites, usually called
Oscar, for Orbiting Satellites Carrying Amateur Radio, provided the
first direct satellite communications between the United States and the
Soviet Union in 1965 when the cold war made it impossible for
governments to achieve this milestone. These satellites were carried into
space during regular government rocket launches. Governments and
private industry make extensive use of satellite technology to create the
radio telecommunications that we now simply expect. The use of
satellites and digital technology enables uninterrupted radio
telecommunication at any time of day over any distance around the earth.
Radio telecommunication has been used to transmit speech between the
moon and earth and to control satellites in deep space. Radio waves,
emitted by all stars, are being used to explore the universe.

Television
Television is simply the transmission of pictures as well as speech and
data by radio waves. Its importance has largely been confined to the
broadcasting industry. With the development of national and
international television broadcasting, which relies on satellite technology,
news and sport now reach most homes in the developed world through
television receivers. However, personal and business communication has
essentially continued with the transmission of speech and data. Teletext
machines now provide access to the transmission of data through
television broadcast signals and pictures are being sent to aid
teleconferencing. The importance of these developments will be
determined by future market needs and the cost of providing them.

As with general radio development, advances in television broadcasting

relied firstly on valve technology and then the invention of
semiconductor devices. As early as the late nineteenth century efforts
had been made to transmit pictures over long distances, but it would take
valve technology to combine these pictures into a moving scene. Unlike
radio, television broadcasting methods could not be researched and
developed until valve technology was discovered. Early designs used an
electromechanical system to capture still pictures and process them as
moving images for radio transmission. The British Broadcasting
Corporation (BBC) broadcast television signals in 1926. These signals
were generated from a mechanical device that captured still images at

Part 2: Telecommunications engineering history of telecommunications 29

 121/2 frames per second and ran them into a moving image. By 1936 this
system had greatly improved clarity and picture stability but was unable
to compete with an all electric system developed conjointly by the
Marconi Company and Electric and Musical Industries (EMI). This all
electric high definition 405 line scanned display system, repeating at 50
frames per second was so advanced in 1936 that it remained the standard
for the BBC until 1985 when it was replaced with a 625 line system
using the phase alternate line (PAL) mode. Australia, where television
broadcasting was not introduced until 1956, commenced services with a
625 line system.

The development of the Marconi EMI electronic system, in

competition with the electromechanical system developed by John Logie
Baird, marked a turning point in the invention and design of scientific
electronic products. Since that time the level of technology and expense
involved in research and development has resulted in the disappearance
of the isolated inventor, replaced by corporately or government funded
teams of engineers and scientists. Modern television is a product of the
same engineering and scientific developments that have provided the
basis for all other telecommunications improvements since the 1930s.
The use of semiconductor technology and improved circuit design to
process ever increasing volumes of data at faster and faster rates has not
only led to improvements in telecommunications but also improvements
in broadcasting.

Turn to the Exercise section and complete exercise 2.8.

Digital communication
Telecommunications are now controlled by computer, or microprocessor,
and are often dependent on the computer as both an input and output
device.

The development of the transistor, which can be used as a high-speed

binary switch, revolutionised the telecommunications industry. The
microprocessor is a direct descendent of the transistor. With the ability
to register two states, on or off, the transistor is the heart of modern
digital electronics.

Clearly, to design complicated control systems to convert information

and speech into a binary code for transmission, and to solve intricate
mathematical problems, thousands of micro-switches are required. The
integrated circuit, developed as a direct result of transistor technology
and now containing thousands of transistors, diodes, and passive
electronic devices, provides the core working system, or central
processing unit CPU, of modern computers and microprocessor devices.

30 Telecommunications engineering
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Other integrated circuits act as memory devices and enable the reliable
and accurate time switching that creates modern multiplexing units.

The ability to send many messages along one conductor with a useful
bandwidth for each message, as is now the case, has come as the result of
several developments; improvements to semi conductors in transistors
and integrated circuits, the use of light as a high frequency carrier, and
the development of optical fibre cable as the travel path for the messages
sent as multiplexed modulated light signals.

The change from analogue transmission to digital transmission is

proceeding now and offers the ability to send and receive far greater
amounts of information more quickly and with greater transmission
quality.

Figure 2.15 Small section of an integrated circuit greatly magnified

The computer as we now know it is an electronic device with input and

output systems and the ability to calculate and store work for further
calculation.
Mechanical methods have been devised to attempt these same tasks.
Before electronics, inventors designed large mechanical machines that,
had they not been too expensive to build, could have provided accurate
mathematical solutions for the scientific world. As late as the early
1800s inaccuracies in mathematical tables were affecting long distance
navigation, resulting in ships losing their way and sometimes being
destroyed on rocks and other objects that could not be accurately located
from the charts of the day. Charles Babbage, a British inventor of
independent wealth, worked on the problem of mechanical solutions to
numerical computation. Over a period of some 30 years from 1822, he
designed three mechanical devices to permit calculation to very fine
accuracy of very large numbers. Principally due to lack of funding these
devices were not able to realise their potential in his lifetime. In 1987 a
replica of his last machine was commissioned by the Science Museum in
London. Construction from Babbages original drawings proved that his
concept would work and could have been made with the machinery
available in the mid nineteenth century. Of course, Babbages machines

Part 2: Telecommunications engineering history of telecommunications 31

 were very complicated and their intricacy required hundreds of hours of
construction. Although these mechanical devices could never have
achieved the multitude of telecommunication tasks now completed by
modern electronic devices they were capable of completing their design
task highly accurate, rapid computation. They also provided the
systems concept by which electronic computers would develop.

The first true electronic computer was developed for the British Secret
Service as a code-breaking device in 1943 during World War II. Valves
and other post office equipment of the time were used to build it.
However every time one of its many valves burnt out, it failed. This
machine combined the concept of a processing system with electronics
but its unreliability and large size demonstrated the need for something
better. Research into semiconductor materials and the development of
the transistor and integrated circuit led to the availability of electronic
components which were the solution to this problem.

Continuing research in semiconductor materials and circuit design has

resulted in dramatic increases in the volume and speed of computer
processing over the last forty years. Machines that took vast amounts of
time and money to develop, controlled power stations and took men to
the moon, are now oversized technological relics when compared to
current home computer systems.

With the microprocessor now in control of telecommunication a variety

of communication systems have developed within the basic transmission
of messages by cable and by electromagnetic waves radio and
television. Whilst television has not, to this stage, been important in the
data transfer industry its significance to commercial broadcasting cannot
be overstated. However, personal and business communication has
essentially remained with radio transmission and cable. The telephone,
and machines such as faxes that use the telephone system, may be linked
by combinations of metal and fibre optic cable and may even rely on
radio transmission along part of the connection between sender and
receiver. Similarly mobile telephone communications, that clearly rely
on radio transmission, may also be carried along fixed cables for part of
their transmission path. The switching that enables the direction of
communication signals to the most efficient transmission path, and
collects many separate signals for simultaneous transmission, is an
unseen part of modern telecommunication systems.

32 Telecommunications engineering
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Caller

Microwaves

Repeater
station

London
Local Telecom
exchange Tower

International
exchange
Earth station

Figure 2.16 Transmitting a long distance telephone call

The World Wide Web

Through computers people are now able to operate their own telegraph
by using the World Wide Web (WWW) and the Internet to search for
news and information and to conduct conversation or written
communication with any person or business anywhere around the world,
all this quickly and for little cost.

Having evolved from cable-linked telegraph to radio to television, we

now find ourselves passing through the same cycle of developments on
our computers, as the Internet grows before our eyes. In 1973,
investigations began in the United States to design systems and
transmission protocols that would allow separately networked computers
to link with each other and thus transmit and share their information with
each other. This was initially inspired by potential military advantages.
By 1986 the major framework of the Internet had been developed by the
National Science Foundation in the United States with the creation of the
NSFNET. Today commercial network providers around the world are
offering additional network facilities and access support, making the
Internet more widely available at costs that are extremely low for the
level of service and information available to the end user. As the Internet
has developed it has become more able to accept different local network
protocols and so a truly World Wide Web is developing. Open Systems
Interconnection (OSI) protocols have greatly increased the availability of
the Internet to providers and users since 1989. In the 1980s about 100
protocols were in use. By 1991 5000 networks in about 40 countries
were linking about 700 000 computers used by an estimated 4 000 000
people.

Part 2: Telecommunications engineering history of telecommunications 33

 Although much of the support for early Internet development came from
the United States Federal Government the development of OSI protocols
opened the Internet to commercial development. Today the bulk of the
system is made up of private networking facilities in business,
educational and research institutions as well as government organisations
around the world. The Coordinating Committee for Intercontinental
Networks (CCIRN) attempts to maintain international cooperation in the
Internet environment. The Internet Activities Board (IAB) was founded
in 1983 and continues to provide various services that manage the day to
day functioning of the Internet. Technical information for prospective
and existing providers, records of user names and system identifiers, and
ongoing research and development are coordinated through the IAB.

Turn to the Exercise section and complete exercise 2.9.

Societal influences
The combined effects of advances in transport and telecommunication
have greatly reduced the time taken to travel between and communicate
with places around the world that are great distances apart. This has
effectively caused the world to shrink, encouraging people to travel for
pleasure and to relocate for work. Families are now spread around the
world instead of being concentrated in local villages and the concept of
the global village has resulted. The priorities that people hold for the
use of their time continue to change and this has resulted in a shift from
the family to the state as the provider of services for the aged, the sick
and the young. The young now constantly question family values while
the old often cannot understand the rate and direction of technological
change that is taking place. In recent times education about technology
as well as in technology has been provided in an attempt to help the
wider community manage the sociological changes that have occurred
with technological development. Some people have questioned the
quality and intention of this information. As well, the ability of the
computer and communication networks to receive, process, store and
distribute vast amounts of information has led to privacy concerns for the
telecommunications industry in general, and the use of computers in
particular. Governments and people are currently facing these problems
and attempting to establish an appropriate division between the public
good and the democratic ideals of freedom and privacy.

Future developments in telecommunications will no doubt see ever

increasing standards in the quality, volume and speed of communication
systems with ever increasing vigilance on the type of information being
collected, processed and provided for communication. With the Web
cam linking sight to other communication forms and increasing

34 Telecommunications engineering
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interactivity it seems just a matter of time before other senses, such as

smell, become a part of the transfer of information by
telecommunication.

Turn to the Exercise section and complete exercises 2.10 and 2.11.

Part 2: Telecommunications engineering history of telecommunications 35

36 Telecommunications engineering
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Exercises

Exercise 2.1

Identify and describe four advances in telecommunications that

followed the invention of the valve.
1 ______________________________________________________
______________________________________________________
2 ______________________________________________________
______________________________________________________
3 ______________________________________________________
______________________________________________________
4 ______________________________________________________
______________________________________________________

Exercise 2.2

Identify and describe four major improvements made to the telegraph

system during its 100 years of international communications.
1 ______________________________________________________
______________________________________________________
2 ______________________________________________________
______________________________________________________
3 ______________________________________________________
______________________________________________________
4 ______________________________________________________
______________________________________________________

Part 2: Telecommunications engineering history of telecommunications 37

 Exercise 2.3

Explain how improvements in telecommunications have allowed

small local business to market themselves nationally and
internationally.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Exercise 2.4

Discuss how the development of hard drawn copper wire assisted the
early development of the telephone and telegraph.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Exercise 2.5

Identify and discuss three effects or influences that the invention of

the telephone has had on society and the community.
1 _______________________________________________________
_______________________________________________________
2 _______________________________________________________
_______________________________________________________
3 _______________________________________________________
_______________________________________________________

38 Telecommunications engineering
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Exercise 2.6

Discuss three possible reasons for the popularity of the mobile

telephone.
1 ______________________________________________________
______________________________________________________
2 ______________________________________________________
______________________________________________________
3 ______________________________________________________
______________________________________________________

Exercise 2.7

Identify four different transmission media that your telephone message

could take to get to someone on the other side of the world.
1 ______________________________________________________
______________________________________________________
2 ______________________________________________________
______________________________________________________
3 ______________________________________________________
______________________________________________________
4 ______________________________________________________

Exercise 2.8

Identify and discuss two reasons why television will remain primarily
a broadcast medium to the end of the twentieth century.
1 ______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
2 ______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________

Part 2: Telecommunications engineering history of telecommunications 39

 Exercise 2.9

Describe three advances in telecommunications that followed the

development of semiconductor materials.
i _______________________________________________________
_______________________________________________________
ii _______________________________________________________
_______________________________________________________
iii _______________________________________________________
_______________________________________________________

Exercise 2.10

Predict the possible outcomes for the inclusion of video as part of

computer communication
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Exercise 2.11

Select the alternative a, b, c, or d that best completes the statement.

Circle the letter.
1 Semaphore is a communication system that:
a requires line of sight
b was used on horseback
c resulted in accurate message transfer
d used electricity for the first time.

2 Ohm defined the relationship between:

a ohms, amps and resistance
b amps, ohms, and current
c voltage, ohms and amps
d none of the above.

40 Telecommunications engineering
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3 Some advantage of wireless communication are:

a no cables need be installed
b cable maintenance is eliminated
c damage to cables does not occur
d all of the above.

4 Which of the following is not an advantage of multiplexing?

a reduce the user cost
b more efficient in the use of resources
c uses more flexible cables
d increase peoples access to telecommunication.

5 The electric telegraph which was the basis of early Australian

telecommunications used the following system to send and receive
messages
a Baudon code
b Morse code
c ASCII code
d Common control.

6 The development of which device revolutionised the

telecommunication industry
a telephone
b resistor
c valve
d transistor.

7 A protocol is
a a first design
b a transmitter
c a rule
d none of the above.

Part 2: Telecommunications engineering history of telecommunications 41

42 Telecommunications engineering
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Progress check

In this part, you have traced the developments that have led to the current
telecommunication technologies and how they have affected our society.
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.

Agree well done

Uncertain

Disagree
Disagree revise your work

Agree

Uncertain contact your teacher

I have learnt about:

historical developments in telecommunications

the effects of innovations in telecommunication on
peoples lives and living standards
environmental implications of telecommunication
systems.

I have learnt to:

research the history of telecommunication in Australia

and understand the way it has impacted on peoples
lives
examine safety issues related to the use of
telecommunication systems.

Extract from Stage 6 Engineering Studies, Board of Studies, NSW, 1999.

Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

In the next part you will examine materials used in telecommunication

engineering.

Part 2: Telecommunications engineering history of telecommunications 43

44 Telecommunications engineering
 helvetica helvetica

Exercise cover sheet

Exercises 2.1 to 2.11 Name: _____________________________

Check!
Have you have completed the following exercises?
Exercise 2.1
Exercise 2.2
Exercise 2.3
Exercise 2.4
Exercise 2.5
Exercise 2.6
Exercise 2.7
Exercise 2.8
Exercise 2.9
Exercise 2.10
Exercise 2.11

Locate and complete any outstanding exercises then attach your

responses to this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your
responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learners Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.

Part 2: Telecommunications engineering history of telecommunications 45

Telecommunications engineering

Part 3: Telecommunications engineering

materials
 Part 3 contents

Introduction ..........................................................................................2

What will you learn?................................................................... 2

Specialised testing..............................................................................3

Copper and other metals used in telecommunications.................. 8

Ceramics as insulation materials............................................... 12

Semiconductors....................................................................... 13

Polymers as insulation materials............................................... 15

Fibre-optics ............................................................................. 18

Exercises............................................................................................25

Progress check .................................................................................35

Exercise cover sheet........................................................................37

Part 3: Telecommunications engineering materials 1

 Introduction

Engineers are interested in the development, properties and availability

of materials and how this can affect design in telecommunication. In
this, the second engineering focus module, you will be studying specific
materials, examining structure/property relationships and investigating
testing procedures as they relate to telecommunication engineering.

What you will learn?

You will learn about:
specialised testing relating to electrical properties
copper and its alloys used in telecommunications
ceramics as insulating materials
the types of semiconductors and their uses in telecommunication
polymers as insulating materials
the types and properties of fibre-optics.

You will learn to:

analyse structure, properties, uses and appropriateness of materials in
telecommunications engineering applications
select and justify materials and processes used in
telecommunications engineering.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

2 Telecommunications
 Specialised testing

Voltage testing
The difference in electrical potential energy between two points is known
as the voltage. The voltage between the ends of a conductor governs the
size of the current flowing through the conductor. This is also known as
the electromotive force that drives electricity in a circuit.

Voltage (V) is measured by a voltmeter and this meter is placed parallel

to the component that it is measuring as shown in figure 3.1. The
voltmeter must have a high resistance compared to the component being
measured otherwise the total resistance of the circuit is reduced and this
changes the value of the voltage being measured. The voltage in both
Direct Current circuits and in Alternating Current circuits can be
measured but different meters must be used.
Resistor

Battery Resistor V Voltmeter

Figure 3.1 Measuring the potential difference across a resistor (note that the
voltmeter is in parallel with the resistor that it is measuring)

A cathode ray oscilloscope (CRO) is one of the most important

measuring instruments used in electronics. Figure 3.2 shows the basic
parts of the CRO. When a DC or AC voltage is applied to the Y-plate
input, the voltage causes the electron beam to bend. This produces a line
on the screen.

Part 3: Telecommunications engineering materials 3

 Evacuated glass tube

Y-plates

X-plates

Electron gun

Electrons in a beam

Fluorescent screen
Spot of light
Figure 3.2 The main parts of a CRO

Have you ever heard of a multimeter? How do think it is different to a

simple voltmeter?
__________________________________________________________
__________________________________________________________

Did you answer?

Did you mention that a multimeter can be used to measure voltage as well as
current and resistance? (multi means many, hence a meter that measures many
things).

Current testing
Current is basically the quantity of electrons moving from one point to
another. Current is measured in amperes (A) and is carried by the
valence electrons in conductors with the electrons flowing from negative
to positive.
1k

Ammeter
reading
Approximately 10 V A 0.01 A
or
10 mA

Figure 3.3 Measuring the current flow in a circuit

4 Telecommunications
 Current is measured by a simple ammeter and it is connected in series in
the circuit. The current flowing through a simple torch globe is about
0.5A. About 10A flows through a fast-boil kettle element. In most low
voltage circuits, like in telecommunication devices, the current flow in
different parts of the circuits is very low and is normally measured in
milliamperes (mA) or microamperes (mA).

The amount of current that flows will vary with changes in voltage and
resistance. This is represented by the formula that you learned during the
preliminary course:
I = V/R or V = IR

As with voltage, current can also be measured by a multimeter. These

are normally only able to measure direct current (current that flows
continually in the one direction) and typically can only measure up to
500mA.

Insulation testing
Suggest reasons why insulation and insulators may be important when
dealing with electricity and electronics.
___________________________________________________________
___________________________________________________________
___________________________________________________________

Did you answer?

Insulation is important for:
protection from electrocution
protection from damage to wires or cables
reduction of energy leakage
reduction of interference from external sources.

If you live in an area that has overhead power lines, you can see the
glazed ceramic insulators that hold the cables at each pole. The pole is
probably made from timber. Another insulating material! If you also
look at the cables that run to the front of your house, you should notice
that they are covered in a plastic polymer coating. Yet another insulator!
All of this has been done to make the current go where it is needed and to
protect us from electrocution. Insulators are also vital in low voltage
circuits. The epoxy printed circuit boards and the outer bodies of various
electronic components are all examples of the use of insulators.

Part 3: Telecommunications engineering materials 5

 Megger testing
Specialised non-destructive tests have been developed to assess the
condition of electrical insulation. The megger test will measure the:
relative amount of moisture in the insulation,
leakage current over the dirty or moist surface of the insulator
winding break-downs or faults as a measure of resistance vs time.

The megger test uses a dc voltage of 500 to 1000 volts applied to the
insulator and current will flow in two ways. Small amounts of current
will be conducted within the structure of the insulator and current may
also flow along leakage paths on the surface. When the voltage is applied
to the insulation, readings are taken of the insulation resistance and
graphed against time. Data should be recorded at the 1 and 10 minute
intervals and at other intermediate times. Only a person experienced
with conducting megger tests can compare the test results with expected
norms because factors like temperature, moisture and previous charge
will all have a significant effect on the results.

This type of test is normally used for large electrical equipment, like
generators and transformers or high voltage cables.

Resistance testing
The insulating qualities of a material can also be simply measured by the
amount of resistance that is offered to the flow of current. A multimeter
is most commonly used to test this resistance. The multimeter has an
internal power source, normally a battery, and when the resistance setting
is selected on the meter, the current is ready to flow through any object
that is introduced to complete the electrical circuit. Simple resistance, on
the multimeter, is used to measure the polarity of components like diodes
and transistors, to check for faults in items like fuses and to identify the
resistance in parts of complex circuits.

For this experiment you will need either a multimeter, if you have access
to one, or a continuity tester.

We can make a simple continuity tester with the following items:

small dry cell battery
two elastic bands
three pieces of wire or three paper clips
torch globe
test items coffee mug, telephone body, metal knife, etc.

6 Telecommunications
 Fit the elastic bands to the battery and the globe in such a way that they
will hold the ends of the bared wire or the straightened out paper clip
onto the terminals of the battery and globe. Attach a wire from one end
of the battery to the globe and another from the globe to act as a probe.
Attach the third wire to the other end of the battery. This is the other
probe. When the probes are connected the globe should glow brightly.
Elastic bands

Probes Lamp
1.5 V Battery
1.5 V

Figure 3.4 Simple continuity tester

Use this continuity tester to complete the table below. Select a few other
items from around the house and record whether the globe glows bright
(B), dull (D) or not at all (N) for these items too.

Item Globe Item Globe

Coffee mug B D N Telephone body B D N

Metal knife B D N B D N

B D N B D N

Those you circled B are good conductors. Conductors have very low
resistance. If you circled D the item offered some resistance.
Insulators didnt let the globe glow at all; they have a high resistance.

Turn to the exercise sheet and complete exercise 3.1.

Part 3: Telecommunications engineering materials 7

 Copper and other metals used in
telecommunications
List the mechanical and physical properties that would be important in
telecommunications conductors.
__________________________________________________________
__________________________________________________________

Did you list the following?

Low resistivity, suitable strength, ductility and ease of joining.

The lower the resistivity of a material, the smaller the amount of

material that is needed to carry current. It also means there are less
insulating materials needed because the wires are thinner, sheathing costs
are lower and transport costs are lower.

To allow the material to be made into wire, it must exhibit ductility.

The material must be able to withstand the tensile stresses applied during
manufacture, extrusion of the insulation and the installation of the cable.

Joining the conductors may be achieved through twisting, soldering or

welding. Some materials are easier to join than others!

In modules that you studied during the preliminary HSC course, you
looked at the structure and atomic bonding of materials. Using this
knowledge, explain why metals are normally conductors and why copper
is an excellent conductor of electricity.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

Did you discuss the metallic bond that has the valence electrons in a cloud
surrounding the ions and that conduction is due to the migration of these
electrons? Did you mention how these free electrons easily transmit the
flow of current?

8 Telecommunications
 Metal ion (positively charged)

Electron (negatively charged)

Figure 3.5 Simple representation of the metallic bond

Of course this theory of current flow is a bit too simplistic and further
development in wave theories has allowed a much clearer understanding
of conductivity. While the individual valence electrons are involved in
the movement of a current, the current moves in the form of a wave and
these waves will move much more easily through a regular arrangement
of obstacles. The regular arrangement of ions in the crystal lattice
structure of an annealed metal, such as the face centred cubic
arrangement of copper, provides little resistance to the passage of the
current waves. Any amount of cold working or the introduction of
alloying elements that sit in the spaces between the ions will increase the
random nature of the obstacles and will increase the resistance of the
material. Heating will cause the ions to vibrate and will increase the
possibility of the migrating electrons hitting an ion and thus being slowed
down. This explains the increase in resistivity noticed when the
temperature of a conductor is raised.

Copper
Copper is the metal that has been traditionally used for communications
wires and cables. It is ductile, has suitable tensile strength and is a very
satisfactory conductor. As a conductor it is second only to silver and if
the conductivity of silver is 100 units then pure copper would measure 97
units. Electrolytic tough pitch copper is used for wires and this grade of
copper has a minimum copper content of 99.9 per cent with around 0.04
per cent of oxygen in the form of an oxide. This level of purity is
essential as the introduction of some alloying elements or impurities can
greatly reduce conductivity. For example only 0.04 per cent phosphorus
will reduce the conductivity by 25 per cent. Other alloying elements, like
cadmium, have little effect on the conductivity. The presence of
cadmium, dissolved in the copper, increases both the strength and wear
resistance of the transmission cable, so it is actually a favourable alloy in
this application.

The manufacturing process used to produce copper wires could easily

induce stress and reduce the conductivity. To overcome this problem,
the cables are cold drawn into wire then the roll of wire is fully annealed.

Part 3: Telecommunications engineering materials 9

 Copper is also an essential part of coaxial cables that are still used for
some applications in telecommunications.
Copper braid
Solid copper

Polymer layer
Polymer skin

Figure 3.6 The structure of coaxial cable

In previous modules you looked at some of the alloys of copper. Some of

these alloys have properties that make them suitable for use in
telecommunications devices.

Name some of these alloys, state the alloying element/s and suggest at
least one use for each.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

Did you suggest sheet cartridge brass (copper with 30 per cent zinc) that could
be used as contacts and cartridge brass cold formed screws and rivets. Even
bronzes (copper with up to 11 per cent tin) could be used where extra strength is
needed. Non-corroding nuts and bolts could be made in bronze.

Aluminium
Aluminium has three advantages over copper when used as conducting
wires. It is lighter, less expensive and more abundant in nature than
copper. With a density of only 2.7g/cm3, compared to 9g/cm3 for copper,
aluminium is specially suitable for aerial power transmission cables.
Only half the quantity of aluminum, by weight, is needed for conductors
with the same resistance. However, it does not conduct as well as copper
(only about 60 per cent of the conductivity of copper) so larger diameter
cables are needed. The larger amount of insulation sheathing needed
offsets some of the savings made on the conductor material.

10 Telecommunications
 On the other hand, aluminium has some inferior properties to those of
copper. These include marginally poorer ductility, tensile strength,
jointing properties and corrosion resistance. This fact has retarded
aluminiums general use in communication cables.

Aluminium alloys are sometimes used for cables. A common alloy

contains 0.5 per cent iron and 0.5 per cent cobalt. These alloying
elements distort the normal aluminium structure and while this increases
the strength of the cable, the conductivity is reduced.

Gold
The conductivity of gold is around that of copper and it is used for the
linkage wires in some semiconductor devices. It is suitable for this
application because while it is very expensive, only small quantities are
used in these miniature circuits. The gold is ductile, doesnt oxidise and
bonds easily to other metals such as aluminium and copper.

Lead
The outer layer on telecommunications cables is known as the sheath and
is designed to create a stable environment for the cable core. Lead was
once used extensively as it has good corrosion resistance, adequate
strength and flexibility and is easy to join. It has been replaced with
polymers because lead suffers from fatigue failures, is heavy and is
relatively expensive. Lead alloys containing antimony and tin were used
to reduce fatigue failures.

Turn to the exercise sheet and complete exercise 3.2.

Part 3: Telecommunications engineering materials 11

 Ceramics as insulation materials
From the information available in previous modules, define a ceramic and
explain why ceramics are often used as electrical insulators.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

Did you mention that ceramics contain both metal and non-metal phases? Did
you also discuss that they often contain both ionic and covalent bonds and that
both these types of primary bonds do not have free valence electrons to allow
for the flow of electrons?

In insulating materials, there is a large gap between the full valence band
and the next electron energy level. For an electron to be free to transmit
a current, it must move up to this next energy level. Under normal
conditions, the gap is so large that electrons are unable to cross.

At high temperatures there is a greater chance that an occasional electron

will possess the energy needed to cross the gap and allow some
conduction.

In ionically bonded materials, ions may migrate, rather than electrons.

This will provide a small degree of conductivity. At elevated
temperatures, ions can become more mobile and conductivity may
increase.

Very high voltages may cause the break-down of some insulators. This
occurs because the electric field is sufficient to raise the energy of some
electrons and free them across the gap allowing electron flow.

Surface breakdown is more common and the presence of moisture or

accumulation of dirt may allow conduction. The glazing of ceramic
insulators helps eliminate moisture because water runs off easily. It also
is less susceptible to dirt build up because it is smooth. The use of a
corrugated design greatly increases the length that the current must
travel.

12 Telecommunications
 Semiconductors
Some materials are known as semiconductors because the gap between
the filled valence band and the empty conduction band is relatively small.
Conduction can occur through two mechanisms. Heating for intrinsic
semiconductors, and doping in extrinsic semiconductors.

Intrinsic semiconductors
Silicon and germanium are semiconductors due solely to the distribution
of electron energies within the pure material. When one valence electron
is freed to cross the energy gap it will mean that one atom within the
crystal lattice only has three bonds as shown in figure 3.7. This gap is
known as an electron hole. The freed bonding electrons are constantly
moving and can even switch from one atom to another. This movement
of the electron in one direction means that the hole moves in the
opposite direction. This could be considered as a positively charged
carrier. Both these movements allow the material to conduct.

Heat may be used to provide the initial energy to free the electron. So, in
contrast to metals, increasing the temperature of an intrinsic
semiconductor will increase conductivity.

B B C

A A

An electron is freed from Electron transfer to A from Electron transfer from C

a covalent bond creating adjacent site,B. Hole to B. Hole moves to C.
an electron hole at A. effectively moves to B.

Figure 3.7 Electrical conduction by the movement of holes

Extrinsic semiconductors
Silicon and germanium have four outer shell electrons per atom but if an
impurity element, that only has three outer electrons is introduced, there
will be electron holes left in the lattice structure. Conduction due to these
holes can occur, and the majority carriers in this type of semiconductor,
are these positive electron holes. Aluminium in silicon is an example of
this type that is commonly known as a p-type semiconductor (p- for

Part 3: Telecommunications engineering materials 13

 positive). These dope atoms are introduced in the ratio of around one
atom to a million base material atoms.

Alternatively, if an element like phosphorus, that has five electrons in its

outer shell, is added to the silicon structure there will be an extra electron
for each phosphorus atom added. Only four of the electrons are bonded
to both the phosphorus and the silicon so the fifth valence electron can
easily move in the conduction energy band and allow conduction to take
place. The electrons are the majority carriers in this type of
semiconductor, so it is known as an n-type semiconductor.

Turn to the exercise sheet and complete exercise 3.3.

The p-n junction

When a piece of n-type semiconductor is joined to a piece of p-type
semiconductor a type of one way valve results. The normal method is
to introduce p-type and n-type impurities into opposite ends of a crystal
of silicon or germanium. At the junction of the two types of materials,
the positive holes in the p-type are filled with electrons from the n-type.
In this region the p-type atoms have gained an electron and are
negatively charged and the n-type atoms have lost an electron and
become a positive ion. This depleted zone has a positive charge on one
side and a negative charge on the other.

When a voltage is applied across the component containing the p-n

junction, it will either conduct or insulate. If the p-type end is made
positive compared to the n-type end then the current will flow easily. If
the voltage is reversed, the positive holes and electrons are attracted
away from the depleted layer and it becomes very hard for charged
particles to move across the junction.
Depletion layer

Forward bias Reverse bias

Figure 3.8 A p-n junction exposed to a voltage

14 Telecommunications
 This simple type of semiconductor device is known as a diode. When
three layers of semiconductor material are combined, npn or pnp, a
transistor is formed. Now you will have an idea of how they work.

These semiconductor devices form the basis of the integrated circuits that
drive the modern telecommunications industry. These devices are
made from wafer thin layers of pure silicon into which the many
individual microelectronic circuits are formed. This chip is then
packaged so that it can be fitted into a printed circuit board and used in
different electronic applications.

Polymers as insulation materials

Drawing on knowledge and understanding that you gained in previous
modules, briefly explain why polymers are insulators. You should refer
to the type of primary bonds found in polymers.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________

Did you answer?

Did you talk about the covalent bonds normally found in polymers and the fact
that all the valence electrons are involved in the bond and are therefore not free
to transmit electrical flow?
Nucleus

Electron

Cl + Cl = Cl2
Figure 3.9 Simple representation of the covalent bond

Many of the insulating materials in personal telecommunication devices

are made from polymers. They are subject to low voltages and low
temperatures and are therefore quite suitable for these applications.

Part 3: Telecommunications engineering materials 15

 If you can find an old broken telephone, pull it apart! If you dont have
an old phone, look at the one in your home and answer the following
activity.

Suggest those parts of the telephone that are made from polymer.
Indicate with an I those parts that must be insulators.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

The body, buttons/dial, receiver are all moulded in polymer. They could
possibly be high impact polystyrene which is a copolymer of polystyrene and
the rubbery polymer, polybutadiene. It doesnt break when you drop it on the
floor! Other tough polymers that would be used for telephone bodies are ABS
(acrylonitrile butadiene styrene) and polycarbonate.
The printed circuit boards (epoxy resin), wire insulation (polyethylene),
integrated circuit bodies (polyurethane) and transistor bodies are all polymer so
that they insulate.

In telecommunication cables, an insulating layer covers the surface of the

conductor material. Traditionally, paper was used to insulate
telecommunication cables and while it has high insulation resistance, if it
gets wet, immediate and complete failure usually results. Paper contains
a high proportion of the polymer, cellulose. Various polymers are
currently used in place of the traditional paper.

Polyethylene
Polyethylene has superior insulation resistance to paper, is suitable for
high frequency cables, can be accurately made to size in a variety of
colours, has good jointing properties and maintains good electrical
properties under humid conditions. Its main disadvantages are cost and
low softening temperature.

When used as an outer sheathing on groups of cables, polyethylene

allows water vapour to penetrate and is difficult to join. For these
reasons it is only used for interior cables or as the outer layer on sheaths
with a wound aluminium foil inner and polyethylene outer.

16 Telecommunications
 Polyvinyl chloride
Polyvinyl chloride (PVC) has poorer electrical properties than either
paper or polyethylene but is tougher, withstands higher temperatures and
survives better in a fire. Under extreme temperatures and combustion,
hydrogen chloride fumes are liberated and may cause corrosion
problems. It is a suitable alternative to polyethyelene.

Polypropylene
Polypropylene has similar electrical properties to polyethylene but is
tougher and has a higher softening temperature. It is not as flexible and
is more expensive than either PVC or polyethylene.

Nylon
Nylon is often used as an insect resistant outer layer or sheath on cables
that are used underground. The hard, smooth surface of the nylon makes
it difficult for an insect or termite to grip the cable.

Turn to the exercise sheet and complete exercise 3.4.

Part 3: Telecommunications engineering materials 17

 Fibre-optics
Light has been used throughout history to convey messages over long
distances.

Identify historical long-distance communication methods that have used

light.
__________________________________________________________

Did you answer?

Did you suggest bonfires and mirrors (using the sun)? What about smoke
signals?

History
Up until the 1840s, both bonfires and mirrors were used to relay
messages from one hilltop to the next. The electric telegraph quickly
replaced these simple light methods as the wires carried the message
regardless of the weather or the terrain.

Light travels very fast, around 300 000 kilometres per second, and it has
long been known that the shorter the wavelength, the more information a
wave could carry. Light waves are only millimetres to nanometres long
and can carry a huge amount of information. Early experiments saw
lasers being fired between towers but fog or rain blocked the message
and it quickly became obvious that the light beam should be guided
through a cable or pipe. Optical fibres were chosen for this purpose.

Typical optical fibres are very fine fibres of glass hairs made of pure
silica. The method of manufacturing optical fibres had been patented
back in the 1930s just in case someone ever finds a use for it. Initially
it was difficult to keep the transmitted light inside the glass fibre but
eventually the glass core was enclosed in a glass sleeve or cladding. The
cladding has a different refractive index to the core and causes the light
energy to be reflected back off the core-cladding interface. This total
internal reflection means that all the light is reflected and continues to
zig-zag along the core of the fibre.

The optical fibres guide the light beam so wherever the fibre goes, the
light follows. These fibres can be made to make the light bend around
corners. Materials used for optical fibres must:
be able to be formed into long thin structures
be flexible enough to go around bends

18 Telecommunications
 allow light to travel through them and so need to be transparent.

Only silica glass and some polymers have these properties.

Buffer coating

Core

Cladding
Figure 3.10 The structure of fibre-optic cable

The light source

The light used in fibre-optic systems is either at or just beyond the red
end of the visible light spectrum. This length of wave is less susceptible
to attenuation in the glass. The light is generated by a little
semiconductor laser (Light Amplification by the Stimulated Emission of
Radiation) made from gallium, aluminium and arsenic. This device
produces a stream of electromagnetic radiation, light, at a constant
frequency. The pulses generated in the laser by the transmitter are sent
down the glass fibre and converted back to electrical impulses by the
receiver.

Movement of light in the fibre

As light beams move down the core of the glass fibre they bounce from
side to side. As long as they only hit the junction between the core and
the cladding at a low angle the total energy of the light rays is reflected
back into the core and none escapes into the cladding. The rays bounce
to the other side and again, as long as the angle is low, bounce back and
continue to be transmitted to the end of the fibre.

Part 3: Telecommunications engineering materials 19

 Total internal reflection
Cladding
Core

Higher refractive Lower refractive

index (n1) index (n2)

Figure 3.11 Movement of light in a fibre

Turn to the exercise sheet and complete exercise 3.5.

Attenuation
Any decrease in the intensity of the light travelling in a fibre is known as
attenuation. Attenuation occurs in glass fibres for three main reasons.
atomic absorption of the light by the glass
the scattering of light by flaws and impurities
reflection of light by splices and connectors.

To overcome this attenuation, the signal is boosted at regular intervals. One

of the advantages of glass fibres over copper conductors is that the signal in
glass travels a lot further without needing boosting. In data networks, for
example, this can be up to 2km without the use of repeaters.

Advantages of optical fibres

One of the other advantages of using glass fibres is their light weight
which means easier installation. For example, a copper coaxial cable can
be replaced by a fibre conductor that is around one-ninth the mass.
Optical fibres also have very wide band widths and this gives large
transmission capacity. Unlike copper, glass fibres arent affected by
electromagnetic interference and because glass doesnt conduct there
arent problems with earth loops. Glass is also suitable in dangerous
environments as it doesnt spark like metals. It is also more secure than
coaxial cable as it cant be spiked to tap off the data signals and certainly
the data being carried is more secure than information transmitted in the
atmosphere. Glass is also inert in corrosive environments, like sea water,
and the raw materials, silica and polymers, are relatively inexpensive.

20 Telecommunications
 Making glass fibres
In Australia, in the early 1970s, the CSIRO experimented with glass
fibres filled with a liquid that had a greater refractive index than that of
the glass. While this worked, these proved hard to make and to handle,
mainly because the liquid leaked out.

Today, optical fibres are generally made by the process of modified

chemical vapour deposition. A pure silicon tube, with a refractive index
of 1.46, is filled with a special gas while being heated by an external heat
source. The gas deposits an inner layer of SiO2 doped with 10 per cent
germanium oxide (GeO2). This lining has a refractive index of 1.47.
The composite tube is then heated to 2 400C and collapsed to achieve a
solid cored fibre.

Turn to the exercise sheet and complete exercise 3.6.

Heat source
approximately
1600C

Fibre material formed

Doped gas by chemical reaction

Silica tube Deposited core

cladding material (solid)

Collapsed preform

Heat source Core

approximately
2000C

Figure 3.12 Production of optical fibre by MCVD (Modified Chemical Vapour

Deposition)

Part 3: Telecommunications engineering materials 21

 Protecting glass fibres
The simplest method of protecting fibres is to pass them through a bath
of molten polymer to form a protective outer skin. To further isolate the
fibre from external forces, a number of methods can be used.

In a loose buffer cable, a loose polymer sleeve is fitted and the gap
between the fibre and sleeve is filled with a gel material. Sometimes
multiple fibres are combined inside a single gel-filled sleeve. This type
of sleeve also provides the fibre with greater insulation from external
heat sources.

Tight buffer cables simply use an extra tight-fitting skin over the initial
fibre coating. A refined form uses a nylon yarn coated with a PVC
jacket.

To protect cables from tensile stress during installation, internal strength

members can be added when multiple fibre cables are constructed. These
members keep the fibres free from stress by minimising elongation and
contraction. Kevlar yarn, glass filled epoxy rods and steel wire can be
used for this purpose. The steel reinforcing is favoured for extreme cold
temperature applications.

Slow feed

Furnace

Thickness monitor
Molten polymer

Polymer bath

Curing oven

Take-up drum

Figure 3.13 Plastic coating of glass fibres

22 Telecommunications
 Fibres in use today
There are two main types of fibres.

Step-index (multimode, single mode)

In a step-index fibre, the refractive index is constant within the core and
it steps to a different, lower value as you move into the cladding. This
type of fibre is available with an 812mm core to allow a single light
beam or with a 50200mm core for carrying multiple beams. This latter
type is known as a multimode carrier.

Multimode carriers allow light to move along the fibre following many
different paths. Some modes take the direct route straight down the
middle while others bounce from side to side all the way down.
Unfortunately the rays from one pulse of light may reach the other end of
the optical fibre at different times. This is known as Intermodal
Dispersion.
Cladding

Core

Figure 3.14 Single mode step-index fibre

Cladding

Core

Figure 3.15 Multimode step-index fibre

Graded index (multimode)

This type of fibre was developed to address the problem of intermodal
dispersion. In this type of fibre, the refractive index of the core changes
from the centre outwards. It has a quadratic profile meaning that the
refractive index of the core is proportional to the square of the distance
from the centre of the fibre. This graded difference in refractive index
slows any modes that travel straight down the centre of the fibre and

Part 3: Telecommunications engineering materials 23

 allows those travelling at the edges to move more quickly. Both modes
are more likely to arrive at the end at the same time. This reduces
intermodal dispersion and improves the output signal.
Cladding

Core

Figure 3.16 Multimode graded-index fibre

Polymer fibres
Certain clear polymers can also be formed into optical fibres but, because
of the much greater attenuation than in glass fibres, all-polymer fibres are
only used on short links up to 100 m in length. Polymer fibres are
usually of the multimode step-index type and are less expensive, more
flexible and easier to handle than glass fibres. Two common polymer
optical fibre combinations are:
1 polystyrene core refractive index of 1.6
polymethylmethacrylate cladding refractive index of 1.49
2 polymethylmethacrylate core refractive index of 1.49
fluoroalkyl methacrylate cladding refractive index of 1.4.

Suggest places where optical fibres are used in modern communications

networks.
__________________________________________________________
__________________________________________________________

Did you answer?

Did you suggest within heavy telecommunication traffic areas like large cities
or over long distances such as between cities and major country centres? What
about near electric rail networks where there is a need for a communication
system that is not interfered with by electromagnetic radiation? How about the
cabling in a media outlet where there is a need for wide bandwidth to cope with
multimedia applications? All these applications now use fibre-optics and the
role of fibre-optics in telecommunications is constantly growing.

Turn to the exercise sheet and complete exercises 3.7 and 3.8.

24 Telecommunications
 Exercises

Exercise 3.1
a With the aid of a sketch, describe how the voltage across a resistor,
in a circuit, would be measured.

______________________________________________________
______________________________________________________
______________________________________________________
b What do the letters CRO stand for and what can you do with this
device?
C ___________________________________________________
R ___________________________________________________
O ___________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c What electrical properties can be measured with a multimeter?
______________________________________________________
______________________________________________________
d List three things about insulators that can be measured using a
megger tester.
i ___________________________________________________
ii ___________________________________________________
iii ___________________________________________________

Part 3: Telecommunications engineering materials 25

 Exercise 3.2
a Complete the table below indicating if you think the item listed
would show high or low resistance when tested by a multimeter.

Item Resistance Item Resistance

Cordless H L Cover on a power H L

phone aerial cord

Circuit board H L Fibre-optic cable H L

base

Polymer radio H L Copper wire H L

body phone cord

b In terms of the properties of copper, give three reasons why it is used

extensively for electrical wires and cables.
i ___________________________________________________
ii ___________________________________________________
iii ___________________________________________________
c Aluminium is also used for electrical cables. Give some advantages
and disadvantages of aluminium as compared to copper.

Advantages Disadvantages

d Why is gold often used for contacts in telecommunication devices?

_______________________________________________________
_______________________________________________________

26 Telecommunications
 Exercise 3.3
a Briefly explain in terms of structure, why some materials are
insulators.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b Germanium and silicon can behave as intrinsic semiconductors.
What is the effect of heat on this type of semiconductor?
______________________________________________________
______________________________________________________
______________________________________________________
c Briefly explain how an extrinsic p-type semiconductor is formed.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
d What is formed when phosphorus is used to dope silicon or
germanium?
______________________________________________________

e Describe, with the aid of sketches, what happens when a voltage is

applied across a p-n junction in two situations.
i When p-end is made positive.
___________________________________________________
___________________________________________________
ii When the p-end is made negative
___________________________________________________
___________________________________________________

Part 3: Telecommunications engineering materials 27

 Exercise 3.4
a With the aid of a sketch, explain how the structure of polymers
means that they are typically insulators.

_______________________________________________________
_______________________________________________________

b complete the table below by suggesting a specific application for

each of the polymers listed.

Polymer Application

polyethylene

epoxy

ABS

nylon

PVC

28 Telecommunications
 Exercise 3.5
a State three traditional methods that have used light to convey
messages over long distances.
i ___________________________________________________
ii ___________________________________________________
iii ___________________________________________________
b Sketch and label the structure of an optical fibre in the space below.

c Briefly explain, with the aid of a sketch, why light moves down an
optical fibre from one end to the other and doesnt escape through
the walls.

______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
d What materials are used to make the type of laser that provides the
light source in a fibre-optic network?
______________________________________________________

Part 3: Telecommunications engineering materials 29

 Exercise 3.6
a What is attenuation?
_______________________________________________________
_______________________________________________________
b Give three reasons why attenuation occurs in glass fibres:
i ___________________________________________________
ii ___________________________________________________
iii ___________________________________________________
c State three advantages of optical fibres over copper cables.
i ___________________________________________________
___________________________________________________
ii ___________________________________________________
___________________________________________________
iii ___________________________________________________
___________________________________________________
d Discuss how early Australian-made optical fibres were different
from those in use today and suggest a problem with these early
fibres.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________

30 Telecommunications
 Exercise 3.7
a Explain one method of making modern glass fibres with the aid of a
sketch/s.
______________________________________________________
______________________________________________________
______________________________________________________

b Briefly outline a method that can be used to protect glass fibres when
they are being installed or when they are in use.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c Explain the difference between step-index and graded index fibres
with the aid of sketches.
______________________________________________________
______________________________________________________
______________________________________________________

Part 3: Telecommunications engineering materials 31

 Exercise 3.8

Select the alternative a, b, c, or d that best completes the statement.

Circle the letter.
1 Current is measured in:
a volts
b watts
c ohms
d amps.

2 Megger testing is used to measure the:

a resistance in electronic components
b insulation onlarge electrical equipment
c current flowing through low voltage circuits
d light intensity in fibre-optics.

3 Which of the following is not used as an insulator:

a mercury
b glazed porcelain
c paper
d polyethylene.

4 Which statement best describes a metallic bond.

a a primary bond where all valence electrons are locked in
b a secondary bond where electrons are free to flow
c positive ions surrounded by a cloud of valence electrons
d attraction between positive and negative dipoles.

5 Comparing aluminium with copper, which statement is correct?

a aluminium is lighter
b aluminium is a better conductor
c aluminium has greater tensile strength
d aluminium joins easily to other metals.

32 Telecommunications
 6 Two elements commonly used as the basis for semiconductor
devices are:
a gold and silicon
b lead and silicon
c germanium and carbon
d germanium and silicon.

7 One of the disadvantages of using polyethylene for insulation on

cables that are to be used outside is:
a water vapour can penetrate the polymer
b it melts when in direct sunlight
c the colour is washed off by rain
d it reacts with the copper that it is protecting.

8 Laser is the abbreviation of:

a light activated switch with emission response
b light amplification by the stimulated emission of radiation
c light application of stimulated emissions of radar
d light across sensitive extrinsic region.

9 Which of the following is not used to reinforce fibre-optic cables:

a kevlar yarn
b glass-filled epoxy
c steel wire
d copper wire.

10 Graded index optical fibres have been developed in an attempt to:

a prevent intermodal dispersion
b minimise attenuation
c provide greater flexibility
d increase resistance to tensile stress.

Part 3: Telecommunications engineering materials 33

34 Telecommunications
 Progress check

In this part you investigated many of the materials used in

telecommunications applications. You have also studied the properties
that make these materials suitable for these applications.
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.

Agree well done

Uncertain
Disagree
Disagree revise your work

Agree

Uncertain contact your teacher

I have learnt about:

specialised testing relating to electrical properties

copper and its alloys used in telecommunications
ceramics as insulating materials
the types of semiconductors and their uses in
telecommunication
polymers as insulating materials
the types and properties of fibre-optics

I have learnt to:

analyse structure, properties, uses and

appropriateness of materials in telecommunications
engineering applications
select and justify materials and processes used in
telecommunications engineering.

Extract from Stage 6 Engineering studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

In the next part you will study the application of mechanics in

telecommunications.

Part 3: Telecommunications engineering materials 35

36 Telecommunications
 Exercise cover sheet

Exercises 3.1 to 3.8 Name: ______________________________

Check!
Have you have completed the following exercises?
Exercise 3.1
Exercise 3.2
Exercise 3.3
Exercise 3.4
Exercise 3.5
Exercise 3.6
Exercise 3.7
Exercise 3.8

Locate and complete any outstanding exercises then attach your

responses to this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your
responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learners Guide to determine what
you need to return to your teacher along with the Mark Record Slip.

Part 3: Telecommunications engineering materials 37

Telecommunications engineering

Part 4: Telecommunications engineering

mechanics and hydraulics
 Part 4 contents

Introduction..........................................................................................2

What will you learn?................................................................... 2

Mechanics in telecommunications...................................................3

Forces and moments ................................................................. 3

Stress and strain ..................................................................... 13

Exercises ...........................................................................................15

Progress check .................................................................................31

Exercise cover sheet........................................................................33

Part 4: Telecommunications engineering mechanics and hydraulics 1

 Introduction

At any one time millions of people are talking to each other across the
globe. At the same time massive quantities of data are being shipped
from computer to computer. Underpinning all this communication is a
fascinating technology that is the focus of the work of the
telecommunications engineers.

There is a network strung out across the globe called the Global
Telecommunications Network. The nodes of this network are computers
programmed to perform as switches. The links of the network are wires,
optical fibres, cables, satellite links and radio channels.

Telecommunication engineers are engaged in the business of designing,

improving, extending, maintaining and operating this network.

This rapidly growing section of the economy is transforming the way in

which health, banking, education, retail, library and many other services
are provided.

What you will learn?

You will learn about:
engineering mechanics and hydraulics as applied to
telecommunications engineering.

You will learn to:

apply mathematical and graphical methods to solve
telecommunication related problems.

2 Telecommunications engineering
 Mechanics in telecommunications

Telecommunications of all types require an intricate and complex

network of cables, wires, optical fibres, repeater stations, transmission
towers and receiving devices. Further, there are broadcasting stations,
satellites and exchanges the list goes on! This extensive infrastructure
involves many types of structures that require the consideration of
mechanics in their design.

In this part we will investigate some ways in which mechanical

principles can be used in the telecommunications industry.

Forces and moments

The application module on landscape products covered:
nature and types of forces
addition of vectors
space and freebody diagrams
resultants and equilibrants
transmissibility of forces
3 force rule for equilibrium
moments of a force
force/couple systems
equilibrium of concurrent forces.

Refer back to the Landscape products module to refresh your memory on

these topics.

Now consider the following:

A power pole with lines attached is used to elevate telecommunication

lines out of reach from the ground. The pole is supported by two stays as
shown in figure 4.1.

Part 4: Telecommunications engineering mechanics and hydraulics 3

 Electrical wire
Stay

Figure 4.1 Power pole supported with two stays

The single pole is commonly used in preference to a trussed section.

1 Can you suggest a reason for this?
_______________________________________________________
_______________________________________________________

The stays and the lines act through a common point on the pole.
2 What is the word given to describe the fact that the lines of action act
through a common point?
_______________________________________________________
3 What is the nature of the force in:
i the wires____________________________________________
ii the pole_____________________________________________

Did you answer?

1 cheaper and simpler construction and installation; less intrusive visually
2 concurrent
3 i tension
ii compression.

Worked example 1

If the tensions in the telecommunication lines are equal to 460 N each

and the tensions in the stays are equal to 375 N each, find analytically the
reaction offered by the ground if the pole and fittings have a combined
mass of 400 kg. The lines make an angle of 10 to the horizontal and the
stays make an angle of 20 to the vertical.
Verify your answer by using a graphical method.

4 Telecommunications engineering
 B
10 10
460 N 460 N
375 N 375 N
20 20

Figure 4.2 Telecommunication lines supported by a pole

Solution

The reaction at the ground will be equal and opposite in direction to the
total of all the vertical components. There will be no horizontal
component to the reaction as the horizontal components of both the lines
and the stays will be balanced by each other.

The vertical component created by the mass will equal the weight.

W = mg

= 400 x 10

= 4000 N

The vertical component created by the lines will equal:

460 cos 10
460 sin 10 10
460 N
375 N

Figure 4.3

V = 2 x 460 sin 10

= 159.8 N

Part 4: Telecommunications engineering mechanics and hydraulics 5

 The vertical component created by the stays will equal:

375 N 20 375 cos 20

375 sin 20

Figure 4.4

V = 2 x 375cos 20

= 704.8 N
Total reaction at the ground = Sum of vertical components
+
SFv = 0
= - 4000 - 159.8 - 704.8 + Rg

Rg = 4.865 kN

This answer can be verified graphically by adding all the vectors acting
on the pole.

You will recall that to add vectors, they must be drawn to scale, and
drawn tip-to-tail.

6 Telecommunications engineering
 460 N Note that the forces are added, one
375 N after the other (in any order) tip-to-
tail. The resultant force is found by
drawing a line from where you
started to where you finished.

The equilibriant is found by closing

the force polygon

resultant
4000 N = 4865 N

375 N

460 N
Figure 4.5 Graphical solution using a force diagram to scale

Turn to the exercises sheet and complete exercise 4.1.

Worked example 2

A television antenna has three guy wires attached to it at point A as

shown in figure 4.4. What tension is required in the third guy wire so
that the resultant of the three forces will act vertically downwards?
Determine the magnitude of the resultant force.

As part of the data supplied, it is common to provide an additional

diagram to indicate correct angles and positioning of the forces.

What is the diagram given as part of the data called?

The answer is below the diagram.

Part 4: Telecommunications engineering mechanics and hydraulics 7

 A

C
40 25 2.2 kN
20
1.3 kN

Figure 4.6 Space diagram of TV antenna on house

Before solving the problem, it is often convenient to summarise the

forces that are acting. This diagram is shown as a sketch (not drawn to
scale) showing the magnitudes of known forces as well as the directions
of each of the forces acting.

What is this diagram called?

The answer is below the diagram.

A

40 25
20

C 2.2 kN

1.3 kN
R
Figure 4.7 Free body diagram of forces acting

A graphical solution is generally the easier method. This is a convenient

method of adding vectors by drawing them tip-to-tail.

Name the diagram that allows the addition of vectors by drawing them
tip-to-tail and to scale.

__________________________________________________________

Did you answer?

A force diagram.

8 Telecommunications engineering
 Graphical solution
45 1 Draw the 2.2 kN force to scale
2.2 kN
and at the correct angle.
2 Draw the 1.3 kN force to scale
and at the correct angle.
3 Draw the directions of the
1.3 kN force C and the resultant, R.
20
R = 5.2 kN 4 The intersection of R and C
will give you the size of these
forces.
40

C = 3.1 kN

Figure 4.8 Force diagram drawn to a scale of 10 mm = 0.5 kN

Mathematical solution

If the resultant force is to act vertically downward then the sum of the
horizontal forces must equal 0.

As there are three forces with horizontal components:

45 40
1.3 cos 20 20 1.3 kN
2.2 cos 45 2.2 kN C C cos 40

2.2 sin 45 1.3 sin 20 C sin 40

Figure 4.9 Three forces with Horizontal components

Part 4: Telecommunications engineering mechanics and hydraulics 9

 Horizontal Resultant (+ ) = Horizontal components of individual forces

= 0

O = 2.2 sin 45 + 1.3 sin 20 C sin 40

1.56 + 0.44
\ C =
sin 40

= 3.11 kN

Vertical Resultant (+
) = S Vertical components

= - 2.2 cos 45 - 1.3 cos 20 - 3.11 cos 40

= -1.56 - 1.22 - 2.38

= -5.16 kN

\ the resultant force is 5.16 kN acting 

Turn to the exercise sheet and complete exercise 4.2.

Worked example 3

An axial force is induced in a mast by two wire stays as shown in figure 4.10.

30 20

A = 1.5 kN B

Figure 4.10 Telecommunication mast with two stay wires

i Find the magnitude of the axial force acting along the mast
ii What is the magnitude of the force acting in the stay wire B.

10 Telecommunications engineering
 O Graphical solution
1 Draw force A to scale.
A = 1.5 kN 30
2 Draw direction of axial force
through the
origin point O.
3 Draw direction of force B
acting at the end
of force A.
B = 2.2 kN
20 4 Add arrow heads, measure
magnitude of B
and axial force.

Figure 4.11 Graphical solution of force acting in mast

Mathematical solution

If the resultant force is to act vertically then the sum of the horizontal
forces must equal 0.
Horizontal Resultant (+ ) = 0
= B sin 20 1.5 sin 30
B = 1.5 x 0.5 / 0.342
= 2.2 kN
Vertical Resultant (+
) = -2.2 cos 20 - 1.5 cos 30
= -2.07 - 1.3
= -3.37 kN (this is the axial force in the mast)

\ the resultant force is 3.37 kN acting 

Turn to the exercise sheet and complete exercise 4.3.

Part 4: Telecommunications engineering mechanics and hydraulics 11

 Worked example 4

The radio tower shown in figure 4.10 is 3 metres square and 15 metres
high. It has a mass of 7 tonnes. It is supported against horizontal wind
loads by four guy wires attached 10 metres above the central base B. Its
effective projected area of 12 m2 is subjected to a horizontal wind
pressure of 650 Pa. When the wind blows from left to right, only one
guy wire AC is active.

Determine:
i tension in the guy wire AC.
ii the reaction at B

30
Guy wire
CG

C B

Figure 4.12 Radio tower

Mathematical solution

The unit of wind pressure is a pascal.

(Remember that 1 Pa = 1 N/m2.)

Pressure = Force
Area

F
650 = 12

= 650 x 12
\ F = 7800 N

This force created by the wind of 7.8 kN can be considered to act through
the centre of gravity.

The centre of gravity for a uniform structure will be half way up the
height. This will be 7.5 metres up for this problem.

12 Telecommunications engineering
 The mass of the tower = 7 T or 7000 kg or 7 x 103

The weight of the tower equals mg = 7 x 103 x 10 N = 70 kN

i tension in the guy wire AC.

Let T be the tension in the cable AC

For equilibrium,

= 0
MB
= (Tsin 30 x 10) 9.5 x 7.8 +(Tcos 30 x 1.5)
T = 9.3 kN

ii the reaction at B
For equilibrium,
(+
) V = 0

RBV - 70 9.3 cos 30 = 70 + 8.1

RBV = 78.1 kN

For equilibrium,

(+ ) H = 0

= 7.8 9.3 sin 30 + RBH

RBH = 3.15

= 3.15 kN 

Part 4: Telecommunications engineering mechanics and hydraulics 13

 Rb is made up of two components
RBH

RB RBV

Figure 4.13 reaction Rb

Rb = (3.152 + 78.12)

= 78.2 kN

tan q = Rbv/ Rbh

= 78.1 / 3.1

q = tan -1 31.65

= 88

\ the reaction at is 78.22 kN at 88 

Stress and strain

The application module Civil structures dealt with:
stress and strain
Youngs modulus.

Revise the theory on these topics for the following worked example.

Worked example 10

A copper wire 3 metres long and of uniform circular cross-sectional area

is stretched 6 mm by the application of a tensile load of 2.5 kN.

Calculate the wire diameter if the modulus of elasticity of the wire

material is known to be 120 GPa.

14 Telecommunications engineering
 Solution

Remember when dealing with stress/strain calculations, the units should

all be converted to MPa, N or mm. Note 1MPa = 1 N / mm2

F = 2.5 kN = 2.5 x 103 N

L = 3 m = 3 x 103 mm

e = 6 mm

E = 120 GPa = 120 x 103 MPa

Modulus of Elasticity = Youngs Modulus, E

E = stress
strain

Fl
E =
eA

Fl
A =
eE

= 2.5 x 103 x 3 x 103

6 x 120 x 103

p d2 10.42
=
4
10.42 x 4
d2 =
p
d2 =
13.27
d =
13.27
= 3.64 mm

Turn to the exercise sheet and complete exercises 4.10 to 4.12.

Part 4: Telecommunications engineering mechanics and hydraulics 15

16 Telecommunications engineering
 Exercises

Exercise 4.1

A power pole with power lines connected is supported by two stays as

shown in figure 4.14. The power lines are tensioned so that they are at
an angle of 15 to the horizontal when the tension in them equals 400 N.

If the tension in each stay equals 380 N, determine mathematically the

reaction at the bottom of the pole if the pole and associated fittings have
a combined mass of 280 kg. Verify your answer by using a graphical
solution.

15 15

400 N 400 N
380 N 380 N
25 25

Figure 4.14 Power pole

Part 4: Telecommunications engineering mechanics and hydraulics 17

 Exercise 4.2

A television antenna has three guy wires, P, R and S attached to it at

point A. What tension is required in the second and third guy wires (R
and S) so that the resultant of the three forces will act vertically
downwards with a magnitude of 6.5 kN?

A
P = 2.2 kN

45 25
S 20
R

Figure 4.15 TV Antenna

Mathematical solution: Graphical solution:

.
0

18 Telecommunications engineering
 Exercise 4.3

An axial force is induced in a mast by two wire stays as shown on figure

2.31.

30 20

A
B = 1.5 kN

Figure 4.16 Telecommunication mast with stay wires

i Find the magnitude of the axial force acting along the mast
ii What is the magnitude of the force acting in the stay wire A?

Mathematical solution: Graphical solution:

.
0

Part 4: Telecommunications engineering mechanics and hydraulics 19

 Exercise 4.4

A radio tower shown in figure 4.17 is 2.6 metres square and 16 metres
high. It has a mass of 6 tonnes. It is supported against horizontal wind
loads by four guy wires attached 10 metres above the central base B. Its
effective projected area of 11 m2 is subjected to a horizontal wind
pressure of 550 Pa. When the wind blows from right to left, only one
guy wire AC is
active.

Guy wire
30

CG

B C

Figure 4.17 Radio tower

a Discuss why only one, or at most two, of the four guy wires will be
active.

20 Telecommunications engineering
 b Find:
i the tension in guy wire AC
ii the reaction at B

Part 4: Telecommunications engineering mechanics and hydraulics 21

 Exercise 4.5

A pay TV satellite dish is attached to the gutter fascia as shown in figure

4.36. The 700 mm diameter dish and single output LNB unit has a mass
of 12 kg and acts at the centre of mass 250 mm from the support pole.
The dish is inclined at an angle of 15.

Figure 4.18 Pay TV satellite dish

231 120 N
N
250

231 120 N 231 N

N

15

W = mg
= 12 x 10
= 120 N
100 mm

Figure 4.19 Free body diagram

If a wind is blowing is with a pressure of 600 N/m2 perpendicular to the

dish and the pole is secured with two bolts 100 mm apart,

Determine:
i the force-couple reaction at the support pole
ii the axial force acting on each bolt. (You may assume that the
magnitude of the axial forces in each bolt will be equal).

Refer to previous work if needed

22 Telecommunications engineering
 Exercise 4.5 cont.

Part 4: Telecommunications engineering mechanics and hydraulics 23

 Exercise 4.6

A simplified diagram of the top of a 50 metre telecommunication tower

is shown in figure 4.20.
15 kN A
4m

15 kN B
C
4m

15 kN D
50 m

E
4m

15 kN F G

H I

80

Figure 4.21 Simplified free body diagram of telecommunication tower

If a wind of 15 kN is acting on radio control units located on joints A, B,

D and F as shown, determine mathematically :
i the magnitudes and nature of the forces in members FG and GI
ii the distance between the legs at the base
iii the total left and right reactions at the base supports, if no other
forces are acting on the tower.

Refer to previous work if needed

24 Telecommunications engineering
 Exercise 4.6 cont.

Part 4: Telecommunications engineering mechanics and hydraulics 25

 Exercise 4.7

The relay units shown in figure 4.22 are common sights throughout the
country in order to establish a mobile phone network. They are usually
located either on buildings or on telecommunication towers. The units
shown are mounted on round pipe and bolted to the sides of a building.

Figure 4.22 Telstra telephone exchange Charlestown

a Discuss the use of round pipe as a support.

_______________________________________________________
_______________________________________________________
_______________________________________________________
b What is the term used to describe a structural member that is
supported at one end only?
_______________________________________________________
c Discuss the forces that would be acting on the bolts that secure the
pipe support to the building.
_______________________________________________________
_______________________________________________________
_______________________________________________________
d How would the engineer decide on what size bolts to use?
_______________________________________________________
_______________________________________________________
_______________________________________________________

26 Telecommunications engineering
 Exercise 4.8

An aluminium wire 3 metres long and of uniform circular cross-sectional

area is stretched 6 mm by the application of a tensile load of 2.5 kN.

Calculate the wire diameter if the modulus of elasticity of the wire

material is known to be 70 GPa.

Part 4: Telecommunications engineering mechanics and hydraulics 27

 Exercise 4.9

Select the alternative a, b, c, or d that best completes the statement.

Circle the letter.
1 Telecommunication towers are often made out of a triangulated truss
assembly. This type of bar assembly is known as:
a an unstable assembly
b a stable assembly
c an assembly containing redundant members
d a structural column.

2 When discussing members in a structural frame, the:

a tie must be a stiff member
b strut needs stiffness as well as strength to take tensile loads
c frame may have some ties in tension and compression
d ties will be in tension and the struts will be in compression.

3 Given that the modulus of elasticity of aluminium is 70 GPa and

copper is 120 GPa, then for a wire to stretch the same amount under
the same load, the diameter of the aluminium wire will be:
a equal to the copper wire diameter
b 1.7 times larger than the copper because Ecopper = 1.7 x Ealuminium
c 1.7 times smaller than the copper because Ecopper = 1.7 x Ealuminium
d approximately 1.3 times larger than the copper wire diameter.

4 A bolt is tightened and used as a connection to join two structural

members together. The bolt may experience:
a a tensile force
b a compressive force
c a shear force
d both tensile and shear forces.

5 A 3 kg telephone, with four rubber feet, is sitting on a table. Each

foot will set a reaction force with the table top equal to:
a 3 kg
b 0.75 kg
c 30 N
d 7.5 N

28 Telecommunications engineering
 6 A 68 cm television set, of mass 30 kg, has legs which are 600 mm
apart in the front view of the television. It is placed centrally on a 1
metre shelf which is supported at each end at A and B. Neglecting
the weight of the shelf, the reactions at supports A and B will be:
a RA = 300 N and RB = 300 N
b RA = 150 N and RB = 150 N

c RA = 15 N and RB = 15 N

d RA = 150 N and RB = 150 N

7 The shear force diagram for shelf and TV set will be:
a b

c d

8 The bending moment diagram for the shelf and TV set will be:
a b

c d

Part 4: Telecommunications engineering mechanics and hydraulics 29

 20 kN A

B C

D E

F G

9 The cross brace members BC, CD, DE and FE in the tower for the
wind load of 20 kN as shown will be:
a redundant (carry no loading)
b in tension only
c in compression only
d in either tension or compression.

10 A rectangular beam, 100 mm wide and 200 mm deep is subjected to

a maximum bending moment of 240 kNm.
If the second moment of area, IXX = 66 x 106 mm4, and the
maximum bending stress is determined by the formula s = My.
I
For the given data, the maximum bending stress will equal:
a 120 MPa
b 180 MPa
c 360 MPa
d 720 MPa.

30 Telecommunications engineering
 Progress check

In this part, you have investigated the mechanics associated with

telecommunication structures.
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.

Agree well done

Uncertain

Disagree
Disagree revise your work

Agree

Uncertain contact your teacher

I have learnt about:

engineering mechanics and hydraulics as applied to

telecommunications engineering.

I have learnt to:

apply mathematical and graphical methods to solve

telecommunication related problems.

In the next part you will examine the application of transmission media
in telecommunications.

Part 4: Telecommunications engineering mechanics and hydraulics 31

32 Telecommunications engineering
 Exercise cover sheet

Exercises 4.1 to 4.9 Name: _______________________________

Check!
Have you have completed the following exercises?
Exercise 4.1
Exercise 4.2
Exercise 4.3
Exercise 4.4
Exercise 4.5
Exercise 4.6
Exercise 4.7
Exercise 4.8
Exercise 4.9

Locate and complete any outstanding exercises then attach your

responses to this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your
responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learners Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.

Part 4: Telecommunications engineering mechanics and hydraulics 33

Telecommunications engineering

Part 5: Telecommunications engineering

electricity/electronics
 Part 5 contents

Introduction..........................................................................................2

What will you learn?................................................................... 2

Principles of telecommunications ....................................................3

Signals and noise ...................................................................... 3

Transmission of images ............................................................17

Baseband transmission.............................................................19

Modulation of carriers ...............................................................20

Transmission media..................................................................30

Evaluating telecommunications systems ....................................46

Exercises ...........................................................................................55

Progress check .................................................................................63

Exercise cover sheet........................................................................65

Part 5: Electricity/electronics in telecommunications engineering 1

 Introduction

In this part we will look at the principles that underpin many of the
telecommunications technologies currently in use, and which are likely to
still be relevant in the context of the new telecommunications
technologies of the future.

What will you learn?

You will learn about:
telecommunications
analogue and digital systems, modulation, demodulation, radio
transmission (AM, FM), television transmission (B/W, colour),
telephony (fixed and mobile), transmission media (cable,
microwave, fibre-optics)
satellite communication systems, geostations.

You will learn to:

describe the basic concepts and applications of modulation and
transmission systems in telecommunications
distinguish the communication bands in the electromagnetic
spectrum
contrast the differences in transmission media
describe the basic principles of satellite communication systems.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

2 Telecommunications engineering
 Principles of telecommunications

Modern telecommunications is one of the fastest changing and most

influential technologies in our society. There are many different formats
and technologies currently in use.

What technologies and applications lie ahead?

While we can do no more than guess what forms telecommunications

will take in ten or twenty years time, history suggests that changes are
inevitable. In ten years time we will most likely take for granted
telecommunications systems that have not yet been invented.

The diversity of current forms of telecommunications prohibits an

exhaustive study of all of them. Furthermore, such a study would not
necessarily give us insights into how newer technologies will work.

Instead, we will look at the principles that have underpinned many of the
technologies currently in use, and which are likely to still be relevant in
the context of the new technologies of the future.

Signals and noise

The performance of a telecommunications network is generally governed
by three simple factors:
the power of the signal being transmitted
the power of the electrical noise in the system
the bandwidth of the system, that is, the range of frequencies that
can be carried.

In this section, we define these basic parameters. We also reinforce the

ideas of analogue and digital signals, and make some simple comparisons
between the two.

Part 5: Electricity/electronics in telecommunications engineering 3

 Analogue signals
An analogue signal is continuously variable in amplitude and time.
Examples of analogue signals include:
the variation of temperature
the amount of water in a dam
the weight of a person.

At each and every instant in time, we can measure an analogue quantity

to any arbitrary accuracy.

Digital signals
A digital signal is one that differs from an analogue signal in two
important aspects:
its amplitude can only be one of a set number of possible levels
its amplitude only changes at regular time intervals.

Digital signals can be obtained from analogue signals by the dual

processes of sampling and quantisation.

Sampling of an analogue signal means taking a series of measurements at

regular instants in time. For example, we might check the temperature
every hour, or measure our weight once a week.

Quantisation is the process of approximating a measurement of

amplitude by the nearest value from a set of possible values. For
example, we might round the temperature to the nearest degree, or our
weight to the nearest kilogram.

The set of possible amplitude values is bounded. That is, there are
minimum and maximum values that we cannot exceed. (This can lead to
errors if our analogue variable exceeds these values.)

Figure 5.1 shows an analogue signal together with a digital

approximation. Note that there are many different possible digital
approximations to a given analogue signal. By varying the sampling rate
and the quantisation interval, we can obtain more or less accurate digital
approximations to the analogue signal.

4 Telecommunications engineering
 Analogue signal

Sampling and
quantisation

Digital signal

Figure 5.1 An analogue signal and a digital approximation to that signal obtained by
sampling and quantisation

Theoretically, a digital signal can take on any number of possible values,

as long as that number is finite. Often, however, the term digital is
(mis)used to describe a system that can take on only one of two possible
values.

A system that can only take two possible values should properly be
called a binary system. Similarly, ternary system can take on three
possible values, while a quaternary system can take on four possible
levels, and so on. Figure 5.2 illustrates binary signals, ternary signals
and quaternary signals.

While binary signaling is simpler to implement, multilevel signaling has

the advantage of being able to send more information per pulse. A
binary signal can indicate one of two possible values at each signaling
interval. A quaternary signal, on the other hand, can represent one of
four possible values at each interval. (An analogue signal has an infinite
number of possible values.)

Part 5: Electricity/electronics in telecommunications engineering 5

 As we shall see later, multilevel signaling can:
send more information per pulse than a binary system
use less pulses to send a fixed amount of information than a similar
binary system.

If our objective is to send information as quickly as possible, then

multilevel schemes can be attractive. Indeed, they are used in most
computer modems and fax machines!
5.0

0.0

5.0

2.5

0.0

5.0
3.3
1.6
0.0
Figure 5.2 Binary, ternary and quaternary signals having two, three and four
possible levels respectively spread across the same 5 Volt range

Turn to the exercise section and complete exercise 5.1.

Time domain representation of a signal

The time domain representation of a signal shows the amplitude of the
signal as it varies with time. This is the type of waveform we would see
if we examined the signal with an instrument called an oscilloscope.

The horizontal axis represents time. Time scales used in

telecommunications applications typically vary between milliseconds per
division to nanoseconds per division depending on the type of signal
being viewed.

The vertical axis is amplitude. This is most often measured in Volts, or

milliVolts.

6 Telecommunications engineering
 Figure 5.3 shows an analogue signal and a (binary) digital signal as
viewed on an oscilloscope. (This particular oscilloscope allows us to
view two signals simultaneously.)

The horizontal scale is 50 msecs (m= 10-6) per division, and the vertical
axis is 1 Volt per division for the upper trace, and 2 Volts per division for
the lower trace.

Figure 5.3 Analogue and digital signals as viewed on an oscilloscope

Figure 5.4 shows the same two waveforms as in the previous figure, but
this time the oscilloscope is set to have an expanded time scale. The
scale is now 500 nsecs (n = 10-9) per division. At first glance we might
not recognise that they are the same signals!

Figure 5.4 Analogue and digital signals as viewed on an oscilloscope with an

expanded time base (note that the digital signal appears to be
analogue)

Part 5: Electricity/electronics in telecommunications engineering 7

 The lower signal the digital signal now appears to be an analogue
signal!

Strictly speaking, all signals are analogue signals. For this reason it is
important to distinguish what we mean by the terms analogue and
digital.

If we have a signal that we assume to be analogue, then we are free to

examine and take measurements of the signal at any instant in time, and
to make those measurements with any degree of accuracy.

If, on the other hand, we assume a particular signal to be digital, then we

should only examine the signal at the mid-point of each interval, and we
should round the signal at that point to the nearest permissible amplitude
level.

Figure 5.5 illustrates how we should examine and interpret a digital

signal. In this case the signal is binary having two possible values 0
and 1.

1 1 0 1 0 0 1 1 0 1 0 1

Figure 5.5 Interpreting a digital signal: we should examine the digital signal at
the mid-point of each interval, shown in this case by the black dots

8 Telecommunications engineering
 Amplitude, period, frequency and
wavelength of a sinusoid
Figure 5.6 shows an analogue signal and a digital signal, with their
amplitudes and periods illustrated.

The amplitude of the analogue signal is normally specified as either a

peak amplitude (that is, from zero to the maximum height) or as a peak-
to-peak value (the amplitude from the lowest point to the highest point).
The units of amplitude are most often Volts.

The amplitude of the digital signal is normally specified simply as a peak

amplitude (that is, from zero to the maximum height). Again, the units of
amplitude are most often Volts.
The period of a wave can be measured via a time domain representation
of the waveform as the time from one point on the waveform, to the same
point on the next cycle of the wave. We usually measure from one peak
to the next, or from one positive zero crossing to the next positive zero
crossing. The units associated with the period are time units (such as
seconds, milliseconds or microseconds).
Period

Vp
Vpp

Period

Vp

Figure 5.6 Amplitude and period of a sinusoidal wave and a digital wave

Another parameter associated with sinusoidal waveforms is the

wavelength. The wavelength is the distance in metres between
equivalent points on successive cycles of a wave as it probigates through
a medium.

(Note the distinction between period and wavelength period is an

interval in time, wavelength is an interval in metres.)

The size of a radio antenna is a function of the wavelength of the signal it

is designed to transmit or receive. Low frequency signals have long
wavelengths and thus require large antennae. In contrast, high frequency
signals have short wavelengths and thus require smaller antennae.

Part 5: Electricity/electronics in telecommunications engineering 9

 Figure 5.7 shows the transmission mast for a radio station with a
broadcast frequency of 1 413 kHz and corresponding wavelength of
212 metres. The antenna height is just over 100 metres, corresponding to
approximately one-half wavelength.

Figure 5.7 Transmission mast for a radio station with a broadcast frequency of
1 413 kHz the height of the mast is just over 100 metres,
corresponding to a one-half wavelength for the frequency used

Figure 5.8 shows an antenna designed to receive frequencies at 2.4 GHz,

or a wavelength of 125 mm. The antenna in this case is approximately
one wavelength long.

Figure 5.8 Antenna for reception of frequencies at 2.4 GHz the antenna is
approximately one wavelength long for that frequency

10 Telecommunications engineering
 The wavelength of a signal also determines its ability to propagate over
and around objects in its path. In general, an object whose principal
dimensions (length or height) are the same as, or larger than, the
wavelength of the signal will effectively block the signal.

Signals with long wavelengths (low frequencies) are only blocked by

large objects (such as mountains). Signals with short wavelengths (high
frequencies) are blocked by both large and small objects (buildings, cars
or trees).

In general terms, this means that higher frequency signals need to have a
clearer path between transmitter and receiver than do signals operating at
lower frequencies. Satellite and microwave links that operate at GHz
frequencies need to have a line of sight between transmitter and receiver.
Even then, they can be affected by atmospheric conditions such as rain.

Lower frequency signals, such as those found in the AM radio band, have
quite long wavelengths of around 200 to 300 metres and hence are able
to find their way around most objects. This is the principle reason that
AM radio offers good reception in most areas.

Turn to the exercise section and complete exercise 5.2.

Noise in a communications link

All telecommunications links contain electrical noise. The term
electrical noise is used to describe any electrical signals that are
undesirable in the system.

The sources of electrical noise are many and varied. Common sources of
electrical noise include interference from other electrical appliances
(such as fluorescent lights and electric drills), nearby lightning, radio
signal interference and faulty connections.

Electrical noise is most often measured in terms of its amplitude relative

to the signals of interest. This is usually referred to as the ratio of the
signal amplitude to the noise amplitude, or simply signal to noise ratio,
or SNR.

To understand the significance of the SNR, think about the situation in a

classroom where you are trying to listen to the teacher. The teacher's
voice, in this case, is the signal. Invariably, there will be other people in
the same room also talking, or whispering: these people are sources of
noise. Your ability to hear the teacher is dependent on the ratio of the
volume of the teacher's voice, and the amount of other noise.

Part 5: Electricity/electronics in telecommunications engineering 11

 If there is no noise, then you should be able to hear the teacher perfectly.
If there is some noise in the room, the teacher will have to speak more
loudly to overcome the background noise. In speaking more loudly, the
teacher is increasing the signal to noise ratio, thus making it easier for
you to listen.

Good electronic design can help reduce the amount of noise that gets into
a circuit. Shielded cables such as coaxial cables, for example, are
specifically designed to reduce the amount of noise that enters a circuit.

Electrical noise that does enter an electrical circuit can distort (or in
extreme cases obscure) the desired signal. You have probably tried to
listen to a telephone call or radio broadcast that was affected by electrical
noise.

A small amount of noise is generally easy to live with. However, in

some applications very large amounts of noise are inevitable: a spaceship
transmitting back to earth from Jupiter can only produce a very weak
signal. The ambient electrical noise is much (much) greater than the
desired signal.

The effect of noise on analogue and digital

signals
We noted above that electrical noise can distort or corrupt an electrical
signal.

If the signal is an analogue signal, it is quite difficult to separate the

signal from the noise. If we amplify the signal, we will also amplify the
noise.

Figure 5.9 shows three signals (or traces) on an oscilloscope. The top
trace is noise induced into an analogue communications link by electrical
interference. The second (middle) trace is the result of that noise
corrupting a sinusoidal signal.

By definition an analogue signal can be examined at any arbitrary instant,

and its amplitude may be any value. Assuming that we do not know
what signal was sent before being corrupted by noise, we cannot separate
the noise from the desired signal. The third (bottom) trace shows the
signal we have to live with.

12 Telecommunications engineering
 Figure 5.9 Effect of noise on an analogue signal we cannot separate the
desired signal from the noise

If the transmitted signal is digital, we can reconstruct the original digital

signal from the noisy received signal without introducing errors (that is,
we can separate the noise from the desired signal)!

Let us consider the situation where a communications channel can

transmit a signal of between 0 and +5 Volts. Let us also assume that
some external interference introduces random electrical noise of up to +/-
1 Volt into the channel. This means that the received signal might be 1
Volt greater or less than the original received signal.

Suppose we now send a binary digital signal over the same channel. We
will use 0 Volts and +5 Volts for the two signal levels. We do not know
at the receiving end what information was sent from the transmitter.
However, we do know that the signal sent must have been either at 0
Volts or at 5 Volts.

When the digital signal is affected by noise, a 0 Volt signal might be

received as -1 Volt or as +1 Volt. Similarly, a 5 Volt signal might be
received as 4 Volts or as 6 Volts. However, it is a trivial matter to
correctly interpret the received noisy signal: we simply decide which of
the two logic levels is closest to the noisy received signal, and replace the
noisy signal with a fresh clean signal of the correct logic level!

If the noise levels are too large, causing a logic 0 Volts to be received as,
say +4 Volts, we will make the wrong decision at the receiving end (by
assuming it was supposed to be +5 Volts) and an error can occur.
However in practice we try to reconstruct the signal before this much
noise accumulates in the signal.

Part 5: Electricity/electronics in telecommunications engineering 13

 This process of reconstructing the original digital signal from a received
noisy digital signal is called regeneration. Regeneration means that as
long as we do not allow too much noise to affect the signal, we can
always rebuild and retransmit digital signals without errors!

Figure 5.10 shows the process of digital signal reconstruction. The upper
trace shows the noise in the channel. The middle trace shows the signal
corrupted by noise, and also the threshold level by which we determine
whether the received signal should be a 0 or a 1. The lower trace
shows the reconstructed signal.

The ability to regenerate signals is one of the key advantages of digital

signals, and makes their use worthwhile even though they require a
greater bandwidth.

Figure 5.10 Reconstruction of a digital signal after corruption by electrical noise

at each sampling instant we simply decide whether the received
signal should be a 1 or a 0

Turn to the exercise section and complete exercise 5.3.

Comparison of analogue and digital signals

We have seen that digital signals allow regeneration, whereas analogue
signals do not.

Do digital signals have any other inherent advantages over analogue

signals?

14 Telecommunications engineering
 The main benefits of digital signals over analogue signals are:
Immunity to noise
As seen in figure 5.10, digital signals can be regenerated prior to
retransmission. This prevents noise from accumulating in the signal as it
propagates through the system, and thus allows long distance
transmission without error. By comparison, noise that is induced into an
analogue signal is accumulated as it propagates through the system.
Cost of digital equipment
The advent of mass produced digital electronic components has
significantly reduced the cost per unit of digital devices. Evolving
technologies have also allowed more complex functions to be
constructed on a single integrated circuit, further reducing costs. By
comparison, analogue devices and circuitry have not been able to
offer similar cost reductions.
Channel capacity utilisation
As communications frequencies increase (into the GHz range), so do
the bandwidths of the available channels. Multiplexing techniques
allow us to take advantage of the increased bandwidths. However, time
division multiplexing (as used in digital systems) is more easily and
cheaply implemented than frequency division multiplexing (as used in
analogue systems).
Security and privacy
Techniques for encrypting signals and data are more easily
implemented in the digital domain than they are in the analogue
domain. This ensures enhanced privacy for sensitive transactions
such as financial transactions that are conducted electronically.
Integration of formats
Some sources of information are analogue, some are digital. If we
wish to simplify our telecommunications systems, it is beneficial to
send all types of data over a common format. It is generally easier to
use digital signals rather than analogue signals as the common
format.

Turn to the exercise section and complete exercise 5.4.

Part 5: Electricity/electronics in telecommunications engineering 15

 The maximum capacity of a communications
link
We have discussed a number of important concepts so far:
the bandwidth of signals
signal amplitudes
electrical noise.

How do these parameters combine to affect the capacity of a

telecommunications system?

Alternatively, is there a maximum limit on the amount of information that

can be sent through a communication link?

The bandwidth describes the range of frequencies that can be sent

through the link. The bandwidth of a communications link is dependent
on its electrical and electronic (and optical) properties.

The signal power is simply the power of the signal that is to be sent
across the link. The noise power is a measure of the electrical noise or
interference that exists in the channel. The ratio of signal power to noise
power is the Signal to Noise Ratio (SNR).

In order to avoid errors in transmission across a channel we should:

try to increase the power of our signals
try to decrease the electrical noise in the system
try to increase the bandwidth of the system.

We will see in the following sections how these key parameters affect the
performance of communications links.

Turn to the exercise section and complete exercise 5.5.

16 Telecommunications engineering
 Transmission of images
Images, or graphical representations, are arguably the oldest forms of
communication. Cave paintings were used by primitive civilisations to
convey impressions and information long before any written language
was used.

Images remain a cornerstone of modern communications. The adage that

a picture is worth a thousand words still holds true for many consumers
of information. We now commonly expect images in our newspapers to
illustrate any story that we may read.

How might we represent images so that they may be telecommunicated?

Most images these days (with the notable exception of photographic

film) use a digital format.

We have already seen how an analogue signal can be converted into a

digital signal via the processes of sampling and quantisation: sampling
takes snapshots of the signal at regular time intervals, while
quantisation assigns one of a finite number of amplitudes or levels to the
signal at each sample.

How does digitisation work for images that are not changing with time,
but are two dimensional and often in colour?

In digitising an image, we do not sample at regular instants in time, but

rather we sample at regular intervals across (and down) the image. That
is, we divide the image into a grid, and represent the whole of the image
by a finite set of regularly spaced samples. Each of the samples is known
as a picture element, which is often abbreviated to pixel. Figure 5.11
shows a digital image sufficiently enlarged to be able to see the
individual pixels.

Figure 5.11 Enlargement of a digital image to illustrate individual pixels

Part 5: Electricity/electronics in telecommunications engineering 17

 The sampling of the image is often measured in terms of the number of
pixels used per unit of distance. The most common units are dots per
inch or dpi. (An inch is approximately 25 mm.) For example, an image
represented on a video display is usually sampled at around 72 dpi.
Modern low cost printers reproduce around 600 dpi. High quality
commercial printers use 1 200 dpi.

The greater the number of dots per inch, the greater the resolution of the
reproduced image. Unfortunately, the higher resolution also requires
more information has to be stored or transmitted.

Having sampled the image, we must now describe each pixel.

For a monochrome (black and white) image we can simply represent

each pixel as being either black or white. This requires only one bit of
information per pixel, saving storage space, but limiting quality image.

For a grey scale image, we describe how light or dark each pixel is to be
via a shade of grey. Most often we quantise the grey scale into 256
different shades. Grey scales convey a more realistic image than does
monochrome, but at the expense of needing more information (8 bits) to
represent each pixel.

If we want to reproduce colour, we need to capture the colour of each

pixel in the image.

The RGB system uses a measure of the relative quantities of Red, Green
and Blue (hence RGB) at each pixel. Since we need to quantise three
colours, we end up with three times as much information as compared
with grey scale images. (That is, 3 x 8 bits = 24 bits for each pixel.)

As an example of the relative sizes of stored images, a typical

photograph (such as the one of the microwave towers later in this text)
digitised at 300 dpi can be saved as:
2 985 984 bits (3 Mb) for 24 bit colour
995 328 bits (1 Mb) for 8 bit greyscale
124 416 bits (124 Kb) for monochrome.

Figure 5.12 shows the relative amounts of data required for each of these
formats. As can be seen, it helps to think closely about whether you
really need colour!

18 Telecommunications engineering
 3.0

Mbits of data required

2.5

2.0

1.5

1.0

0.5

0
24 Bit RGB 8 Bit Grey Scale 1 Bit
Colour Monochrome
Figure 5.12 Relative amounts of data required to represent an image as colour,
grey scale and black and white

Baseband transmission
The term baseband is used to describe a telecommunication system in
which the message to be sent is converted directly to an electrical signal,
and is then sent over a cable to its destination. The frequency range of
the transmitted signal is identical to the frequency range of the original
signal.
(This contrasts with systems such as microwave and radio that, as we
will see, use modulation of a carrier wave to transmit information at
frequencies different to the original signal.)
Baseband systems are very common. If you connect two PC's together
with a serial cable, you are creating a baseband link. The keyboard is
connected to a PC via a baseband link. A (wired) intercom system is a
baseband link.
The advantage of baseband systems is simplicity. All that is required for
a baseband link is to convert the signal to be transmitted from its original
format into an electrical signal at the sending end, and to convert it back
to its original format at the receiving end.
For example, speech can be converted into an electrical signal using a
microphone, and converted back into sound using a loudspeaker. The
wire joining the two ends is a baseband link.
The fundamental disadvantage of baseband signals is that they are usually
only suitable for transmissions over short distances. While a simple wire
connection works well across a room, it is not suitable for connection
across the world. The lengths of wire needed, the fading (attenuation) of
the signal along the wire, and the susceptibility to introduced electrical
noise make long distance baseband transmission impractical.

Part 5: Electricity/electronics in telecommunications engineering 19

 Modulation of carriers
The concept of modulation is fundamental to telecommunications
systems.

As a simple description, modulation involves piggybacking information

on to a carrier (or transportation) wave. You might think of the carrier
wave as a truck, and the information, or message signal, as the goods to
be carried on the truck.

Carrier waves are better suited to transmitting signals over long distances
than are baseband systems. This is because we are free to choose the
frequency of carrier wave that best suits the medium over which we are
transmitting.

For example, if we wanted to transmit speech over a radio link using

baseband frequencies, we would have to broadcast frequencies of around
300 Hz to 3500 Hz, with resulting wavelengths of hundreds of kilometres
long. Hence for efficient transmission we would need antennas that were
25 kilometres high!

By modulating the signal to higher frequencies for radio transmission, we

can take advantage of shorter wavelengths, and hence smaller antennae.

In any modulation system, we need to have three components:

a carrier wave
a message (or information) signal
a method for piggybacking (or modulating) the message signal
onto the carrier wave.

Carrier waves
The carrier wave is simply a pure sinusoidal wave at some predetermined
frequency. A carrier for AM radio is the same as a carrier for FM radio,
microwave or satellite links: only the frequency changes.

Table 5.1 shows the range of frequencies used for carrier waves, and
their common designations. Table 5.2 shows the frequency ranges of
some familiar applications.

20 Telecommunications engineering
 Carrier Frequency Range Common Description

3 30 kHz Very Low Frequency (VLF)

30 300 kHz Low Frequency (LF)

300 3000 kHz Medium Frequency (MF)

3 30 MHz High Frequency (HF)

30 300 MHz Very High Frequency (VHF)

300 3000 MHz Ultra High Frequency (UHF)

3 30 GHz Super High Frequency (SHF)

30 300 GHz Extremely High Frequency (EHF)

Table 5.1 Carrier frequencies and their common designations

Application Carrier Frequencies

AM radio 526.5 1606.5 kHz

FM radio 88 108 MHz

HF CB and marine radio 26.965 27.980 MHz

Remote garage door openers 304 MHz

VHF television 45 230 MHz

UHF television 520 820 MHz

Mobile telephones 820 915 MHz

Microwave links 3 30 GHz

Satellite links Various between 1 GHz 100 GHz

Table 5.2 Carrier frequencies of some common applications

The carrier frequency is often used to designate different radio stations.

For example, Triple J (FM) in Newcastle uses a carrier frequency of
102.1 MHz. 2NUR-FM (the radio station at the University of Newcastle)
uses a carrier frequency of 103.7 MHz. ABC Local radio in Newcastle
(on the AM band) uses a carrier frequency of 1233 kHz.

Having established a carrier wave as a means of transporting a message,

we now need to consider how to piggyback our message onto the
carrier. Figure 5.13 shows a sample information (or message) signal,
together with a carrier wave.

Part 5: Electricity/electronics in telecommunications engineering 21

 Message signal

Carrier wave
Figure 5.13 Modulating wave and carrier wave the inputs to a modulator

Amplitude modulation

Basic technique of amplitude modulation

In amplitude modulation we vary (or modulate) the amplitude of the
carrier wave.

Figure 5.14 shows the amplitude of a carrier wave being modulated by a

triangular signal. Notice that the frequency of the carrier wave is
constant, but that the amplitude of the carrier varies to reflect the
triangular modulating signal.
Message signal

Amplitude modulated wave

Figure 5.14 Amplitude modulation of a carrier wave by a triangular signal

22 Telecommunications engineering
 Figure 5.15 shows a voice-modulated AM wave. The voice signal has a
frequency of around 100 Hz. The AM wave has a carrier frequency of
1 233 kHz. The ratio of these two frequencies means that there are about
12 000 cycles of the carrier wave for each cycle of the modulating wave.
Hence we cannot see the individual cycles of the carrier in this figure
we can only see the outline, or the envelope, of the modulated carrier.

Figure 5.15 Oscilloscope display of a carrier wave being amplitude modulated

by a voice signal this signal is actually from an AM radio
broadcast

One way that the modulation process can be achieved is by multiplying

the carrier wave with the message signal as shown in figure 5.16.
Carrier wave

Amplitude
modulated
signal

Modulating wave
Message signal)

Figure 5.16 Multiplication of a carrier wave by a message signal to give an

amplitude modulated (AM) signal in this case the modulating
signal is a digital waveform

Part 5: Electricity/electronics in telecommunications engineering 23

 Demodulation is the process of separating the message signal and the
carrier wave at the receiving end.

The principle advantage of AM systems is the simplicity with which the

received signal can be demodulated. This is a very significant factor

We only need one modulator to transmit an AM broadcast, but we need

many demodulators to receive the signal (one inside each radio receiver
picking up the broadcast). Hence the cheaper we can make
demodulation, the more people will be able to afford to receive the AM
broadcasts. This aspect was a prime benefit of AM transmission before
low cost electronic technologies were evolved.

The trade-off for relatively low cost AM transmission is the quality of

sound.

Because the envelope of an AM signal is always varying, the average

amplitude is significantly less than the peak amplitude. This means that
the signal to noise ratio (SNR) is less than could be achieved if the carrier
amplitude was constant.

AM demodulation can be achieved with a very simple envelope

detector circuit shown in figure 5.17.

A diode is used to select only one half of the amplitude modulated signal
(in this case, the positive half). A resistor and capacitor together form a
smoothing filter that extracts the envelope of the signal from the
modulated carrier. The envelope is the original message signal.
Signal rectification

AM signal

Smoothing filter

Baseband signal
Diode

Envelope detector

Figure 5.17 Simple envelope detector circuit for demodulation of AM signals

the incoming AM signal is rectified to extract the positive half only,
and then smoothed to extract the envelope of the signal

24 Telecommunications engineering
 AM applications
Amplitude modulation is used primarily for speech communication via
radio. The simple modulation and demodulation processes provide low
cost receivers. Radio broadcasting (on the AM stations) and CB radios,
as shown in figure 5.18, both use amplitude modulation techniques.

Figure 5.18 A low cost CB radio that uses amplitude modulation to convey a
message over a 27 MHz carrier

Frequency modulation

Basic technique of frequency modulation

As the name might suggest, frequency modulation involves varying the
frequency of the carrier wave in order to convey information.

Figure 5.19 shows the frequency of a carrier wave being modulated by a

triangular signal. Notice that the amplitude of the carrier wave is constant,
but that the frequency of the carrier changes with time. The frequency of
the carrier is lower where the message signal amplitude is low, and the
carrier frequency is higher where the message signal amplitude is higher.
Message signal

Frequency modulated wave

Figure 5.19 Frequency modulation of a carrier by a triangular signal

Part 5: Electricity/electronics in telecommunications engineering 25

 AM has the inherent disadvantage that the average amplitude of the
resulting modulated carrier is always less than the peak amplitude, thus
reducing the signal to noise ratio. FM techniques overcome this problem
since the amplitude of the FM signal is always at its maximum value.
That is, the average signal to noise ratio (SNR) of FM transmission is
superior to that of AM.

Unlike AM which uses a single carrier frequency, FM modulation uses

frequencies at and around the nominal carrier frequency. This means that
an FM signal occupies a greater bandwidth than does an AM signal. This
wider bandwidth means that FM offers greater channel capacity than is
available with AM techniques.

The circuitry required for modulation and demodulation of FM signals is

generally more complicated, and hence more expensive, than those
circuits used for amplitude modulation. This factor limited the
widespread adoption of FM broadcasting for a number of years in
Australia until more cost effective electronic circuits could be devised
and manufactured.

FM applications
Frequency modulation is used for speech, music and data transmissions,
primarily using radio links. Radio broadcasting using FM techniques
provides a better sound quality than is obtainable from AM broadcasting.

Television stations also use FM techniques to broadcast the soundtrack to

the programs. The carrier frequencies used for television sound are very
close to the carrier frequencies used for the vision signal.

Phase modulation
Phase modulation, or PM, varies the instantaneous phase (or angle) of
the carrier wave to represent the message. PM can be and is used, though
primarily only for specialised applications. A PM signal has a constant
amplitude waveform like FM, but requires less bandwidth.

Turn to the exercise section and complete exercise 5.7.

26 Telecommunications engineering
 Digital modulation techniques
The modulation schemes described above are analogue or continuous
wave modulation techniques. That is, both the carrier wave and the
message signal are analogue signals.

In many applications we want to be able to transmit digital data over a

modulated link.

Digital modulation techniques modulate an analogue carrier with a

digital signal in order to transmit digital data. The concept is surprisingly
easy to understand having already seen analogue modulation techniques.

The terms Amplitude Shift Keying (ASK), Frequency Shift Keying

(FSK) and Phase Shift Keying (PSK) are used to describe the digital
variants of AM, FM and PM respectively.

Amplitude Shift Keying

Amplitude Shift Keying involves switching the carrier wave between two
different amplitudes. In its most simple form, we simply have full
amplitude and zero amplitude as the two levels. Figure 5.20a illustrates a
binary ASK waveform.

In more sophisticated systems, multilevel ASK is used. This allows us to

represent more than one bit of information for each signaling level. For
example, if we use four different amplitude levels, we can encode two
bits of information in each signaling interval. Eight amplitude levels
allows three bits of information per signaling interval.

Frequency Shift Keying

In Frequency Shift Keying we use two or more different carrier
frequencies to convey digital data. When we have two frequencies we
can arbitrarily assign one frequency to a logic High and the other
frequency to a logic Low. If we use four different frequencies we can
represent two bits of information per signaling interval. Figure 5.20b
illustrates a binary FSK waveform.

Phase Shift Keying

In Phase Shift Keying we use different phases of the carrier wave to
convey digital data. For binary digital data, we simply invert the phase
of the waveform at each transition between logic levels. Figure 5.20c
illustrates a PSK waveform.

Part 5: Electricity/electronics in telecommunications engineering 27

 Message signal

Amplitude Shift Keying

Frequency Shift Keying

Phase Shift Keying

Figure 5.20 Digital modulation techniques: a Amplitude Shift Keying (ASK); b

Frequency Shift Keying (FSK); c Phase Shift Keying (PSK)

More sophisticated keying schemes

In practice, we often use several keying schemes concurrently. For
example, the combination of ASK and PSK is commonly used in modem
and fax machines.

The various modem standards such as V.33, V.34 and V.90 specify how
many combined amplitude and phase keying levels are to be used to
represent digital data.

Table 5.3 shows the maximum data rate, the number of different
amplitude/phase levels, and the number of bits of information
represented in each signaling interval, for a number of modem standards.

28 Telecommunications engineering
 Standard Data Rate Number of different Number of bits per
ASK/PSK levels signaling interval

V.32 9,600 bits per sec 32 5

V.33 14,400 bits per sec 128 7

V.34 28,800 bits per sec

V.90 56,000 bits per sec

Table 5.3 Common standard modem specifications

Turn to the exercise section and complete exercise 5.7.

Part 5: Electricity/electronics in telecommunications engineering 29

 Transmission media
In this section, we look at some of the common types of transmission media
used in telecommunications, and identify their advantages and disadvantages.

However, before looking at particular examples of transmission media it

is helpful to consider the electromagnetic spectrum from which all
signals are derived.

The electromagnetic spectrum

The electromagnetic spectrum describes all of the frequencies used for
telecommunications.

We saw previously, in table 5.3, that various frequency ranges are given
particular names. For example, HF describes the High Frequency band
from 3 to 30 MHz. UHF represents the band from 300 MHz to 3 GHz.

In Australia, and indeed around the world, the electromagnetic spectrum

is divided into various bands for particular applications. These
applications include:
aeronautical navigation
broadcasting
land mobile transmissions
maritime mobile
meteorological aids
radio navigation
satellite communications
amateur radio.

The administration and supervision of broadcasting in the

electromagnetic spectrum is very closely monitored by government
authorities. It is illegal to transmit in bands for which you are not
licensed.

With increasing demand for access to telecommunications systems,

available space in the electromagnetic frequency spectrum is becoming a
scarce resource. One way we can create more frequency spectrum is by
using increasingly higher frequencies. This in turn brings its own
technological problems.

Another way to address the problems of limited resources is to make

better use of the currently used bands. Essentially this means squeezing

30 Telecommunications engineering
 more users into the available frequency bands. This is where techniques
for reducing the required bandwidth for a signal become important.

You may have heard of discussions both here in Australia and overseas
about auctioning off parts of the spectrum to the highest bidder. Radio
broadcasting and mobile telephones are probably the two most common
areas where new operators are seeking to gain access to the allocated
frequency bands.

Literally billions of dollars have been paid for nothing more than the
right to use certain frequencies! The electromagnetic spectrum has
become a commercially valuable commodity! (Who owns the
frequency spectrum anyway?)

If you have access to the Internet visit the following sites:

<http://www.aca.gov.au/frequency/index.htm> for more details regarding the

allocation of the radio frequency

<http://www.aca.gov.au/frequency/arsp-wc.pdf> to view a chart of the

different frequencies and their applications (accessed 04.12.01).

The reference pages of electronic store catalogues (such as Dick Smith

and Jaycar) also contain descriptions of the broadcast bands.

Figure 5.21 shows a simple overview of the electromagnetic spectrum.

Band VLF LF MF HF VHF UHF SHF EHF

Frequency (Hz) 104 105 106 107 108 109 1010 1011 1012 1013 1014

Tele-
Music vision
Mobile
Radio phones Optical
Speech fibres
AM FM Microwave
radio radio
Satellite Infrared
Twisted pair cable

Mains wiring Coaxial cable

Waveguides

Wavelength 105 104 103 102 101 100 101 102 103 104 105 106

Figure 5.21 Overview of the electromagnetic spectrum

Part 5: Electricity/electronics in telecommunications engineering 31

 Classification of media
In practice, transmission media can be divided into two broad groups:
guided and unguided (or free space) media.

Guided media, as the name implies, refers to transmission media that

carry signals along a conductor. Examples include telephone wires and
optical fibres. Guided media share the common characteristic of
requiring a physical link between the sending and receiving ends of the
communications link. That is, a cable must physically connect the two
ends. This is not a problem over short distances, but can result in
expensive infrastructure across long distances or difficult terrain.

Unguided (or free space or wireless) media transmit their signals through
air and/or space. The signals are not guided by any physical conductor.
Unguided media have the obvious advantage of not needing a physical
connection, and hence are very suitable for communications over water
or difficult terrain and long distances.

Guided media
Cables are the principal media used for guided transmission. Cable types
used include twisted pair cable, coaxial cable and optical fibres.
Another medium used for guiding electromagnetic radiation is called a
waveguide.

The principal characteristics that distinguish various types of guides

include:
bandwidth we have seen that the capacity of a channel to convey
information is directly proportional to the channel bandwidth.
signal attenuation signals travelling along a cable are subject to
attenuation, or reduction in amplitude. This attenuation results from
current flowing in the cable interacting with the resistance of the
cable resulting in some power loss in the signal. We have already
seen that the capacity of a channel is dependent on the signal
amplitude.
interference noise is induced in a cable from electromagnetic
interference from external sources. Increasing noise in a cable
decreases the signal to noise ratio, and hence reduces the channel
capacity of the cable.
cost quite clearly everyone tries to reduce the cost of their projects.
In telecommunications we try to use the lowest cost cable that still
performs to the required specifications.

32 Telecommunications engineering
 Twisted pair cable
A twisted pair cable is simply two parallel insulated copper wires that
are twisted together in a spiral pattern. The interweaving is done to help
reduce the electrical noise that is induced into the cable from external
sources.

In many instances, multiple pairs of wires are bundled together into a

single cable, and encased by a tough protective sheath. Such a bundle
might contain hundreds of pairs.

Twisted pairs are probably the most common medium in use today.
They are used for both analogue and digital signalling, and are used
extensively in the telephone network, principally for the final stage of
connections to homes.

Twisted pair cables can accommodate frequencies up to around 1 MHz,

or even up to 10 MHz for short distances.

Attenuation rates are of the order of 3 dB per kilometre, equating to a

reduction of signal amplitude of 0.5 for each kilometre of cable.
Repeater stations, used to boost the signal levels after attenuation, are
spaced at around 2 km intervals.

While the twisting does reduce susceptibility to interference, twisted

pairs have only moderate immunity to interference. For some special
applications, an electrical shield consisting of a thin metal foil is placed
around each twisted pair to further improve noise immunity. Such cables
are known as shielded twisted pairs.

Twisted pair cabling is relatively easy to work with, and is quite

inexpensive.

Coaxial cable
A coaxial cable is comprised of two concentric conductors separated
internally by an insulating dielectric material. The concentric
construction means that coaxial cables are much less susceptible to
external noise sources than are twisted pairs.

Coaxial cables can accommodate frequencies up to around 100 MHz, and

up to 1 GHz for shorter distances. As such, they are much better suited
to carrying modulated signals (such as television) and high speed digital
signals than are twisted pairs.

Attenuation rates for coaxial cables tend to be higher than for twisted
pairs. Typical values are of the order of 7 dB per kilometre. Repeater

Part 5: Electricity/electronics in telecommunications engineering 33

 stations spacings depend on the frequencies used, and can vary from
between 1 km to 10 km.

Coaxial cabling is moderately easy to work with, and is moderately

inexpensive. Special (though inexpensive) tools are required to properly
join and connect cables.

Figure 5.22 shows examples of various types of cables.

Figure 5.22 Examples of cable types, including from top to bottom: optical fibre
with terminating connector; coaxial cable; shielded twisted pair,
mains cable

Optical fibres
Optical fibres are simply strands of glass, surrounded by cladding and
sheaths to contain the light in the core, and to protect the delicate fibre
from breakage. They are lighter and thinner than twisted pair and coaxial
cables.

Often, many fibres are bundled together in much the same way as twisted
pairs. The additional infrastructure cost of running multifibre cable is
more than offset by the additional capacity provided by the additional
fibres.

Optical fibres have excellent immunity to induced noise. Because optical

fibres only conduct in and near the visible light spectrum, interference
from other parts of the spectrum (such as radio waves and 50 Hz power
supply noise) is not a problem. The only source of interference is from
other light entering the cable and this is unlikely since the fibre is
encased in an opaque sheath.

34 Telecommunications engineering
 Optical fibres have a frequency range of between 180 and 370 THz
(TerraHertz, that is, 10 12 Hz). This results in a very large useable
bandwidth, and hence immense channel capacity.

The attenuation of signals in optical fibres (around 0.5 dB per km) is

significantly less than that found in coaxial and twisted pair cables. This
results in less need for repeater stations.

The only significant disadvantage of optical fibres is the difficulty of

terminating and repairing damaged cables. Such tasks require the use of
expensive equipment. For this reason, installation of optical fibres into
individual homes and workplaces is not (yet) an economically viable
proposition.

Optical fibres are used almost exclusively for digital applications.

Signalling is almost exclusively based on a binary (on-off) system.

Mains wiring
While mains wiring may not obviously be part of a telecommunications
system, it is used for some specific applications. Perhaps the most
common of these is to control the switching of off-peak hot water
systems.

You might know that off-peak hot water systems are used to distribute
the load on the power grid so that the generating stations can run closer
to constant load conditions at all times. In order to be able to control the
load on the power stations, we need a way of switching hot water
systems on and off.

The most common method for controlling the switching is called audio
frequency injection or ripple control. This technique involves sending
coded pulses of audio frequency signals along the power lines. The
signaling frequencies used around 200 to 300 Hz are in the audio
frequency range, hence the name audio frequency injection. Different
frequencies are used by different distribution authorities so as not to
interfere with one another.

This scheme is actually Amplitude Shift Keying. The carrier wave is a

200 300 Hz tone, while the message signal is the coded signal to tell
particular hot water systems to turn on or off. A frequency sensitive
detector in the electrical switchboard is tuned to the particular frequency
used, and operates a switch supplying power to the hot water system.

You may have heard some strange noises coming from electrical
appliances in your home late at night and very early in the morning.
These times correspond to the times that off-peak hot water are turned on
and off respectively. The noises you can hear are the coded pulses

Part 5: Electricity/electronics in telecommunications engineering 35

 flowing in the various appliances in your home. Some appliances are
more susceptible to emit the audio signals than others.

Figure 5.23 shows a ripple control unit mounted in a domestic switchboard.

Figure 5.23 Ripple control unit on the right hand side is designed to detect and
interpret audio frequency signals injected onto mains wiring to
control an off-peak hot water system

Waveguides
Waveguides are a special type of 'cable' used for high frequency signals.

You might recall from our discussion of power line conductors in

Personal and public transport that electrical current has a tendency to
concentrate close to the surface of conductors, and not to be uniformly
spread across the cross-section of the material. This effect was termed
the skin effect.

The skin effect is dependent on frequency: the higher the frequency, the
more tendency there is for the energy to be concentrated on the surface.
At very high frequencies, the energy all but escapes from the conductor,
and instead propagates in free space around the conductor.

A waveguide, as the name might suggest, is simply a means of guiding

electromagnetic energy in a particular direction.

Typically a waveguide is a rectangular metal tube (hollow in the middle).

The dimensions vary according to frequencies being used, but
dimensions of tens of centimetres by centimetres are typical.

36 Telecommunications engineering
 Applications of waveguides are quite specialised. Places where they are
often found include military and air traffic control radars (have a look
next time you are taxiing around Sydney Airport), and high powered high
frequency transmitters (such as television towers).

Figure 5.24 Some laboratory waveguide equipment the device on the left is
used for measuring microwave frequency; the horns on the right
hand side are antennae used to transmit and receive microwave
signals

Table 5.4 summarises the key parameters for the various types of cable.

Cable type Useful distance Frequency range Typical applications

Twisted pair 2 km 0 10 MHz baseband signals,

telephones, office
LANs

Coaxial 1 10 km 0 1 GHz modulated signals,

high speed digital

Optical fibre 40 km 180 370 THz very high speed digital

Waveguides 10 m 3 30 GHz radar, high power

transmitters

Mains wiring 50 km 0 400 Hz ripple control

Table 5.4 Summary of principal cable types used in telecommunications

Part 5: Electricity/electronics in telecommunications engineering 37

 Unguided media
Unguided media is the general term used to describe communication
links that are not physically connected. The term wireless is often used
in such cases.

Wireless links are becoming increasingly popular in a range of

applications as a result of the flexibility they offer. For example, infrared
links between computers and peripherals eliminate the need for unwieldy
cables. Mobile telephones have revolutionised the way we think about
personal communications.

The principal characteristics used to describe unguided media include:

frequency the frequencies used for wireless links range from
around 10kHz (for submarine radio communications) to 200 GHz for
some satellite communications.
range the effective range of wireless links varies from around 10
metres (for infrared and Bluetooth) technologies, to tens of
thousands of kilometres in satellite applications.
directionality some links are designed to be point-to-point (such as
in microwave links) and others are used in broadcasting to many
receivers.
half- or full-duplex communications half-duplex communications
refers to a link in which the information flow is in one direction
only. A full-duplex link allows information to flow in both
directions.

Radio
The term radio is most often used to describe non-directional transmissions in
the spectrum range from 3 kHz to 1 GHz. Both half- and full-duplex systems
are used. Applications of radio to telecommunications include:
AM Broadcasting
The AM broadcast band in Australia extends from 526.5 kHz to
1606.5 kHz. This band is divided into separate sub-bands (or
frequency slots) for each radio station.
Each frequency slot has a bandwidth (or range of frequencies) of 9
kHz. This means that the existing AM band can accommodate up to
120 different broadcast stations without replicating frequencies. The
9 kHz bandwidth of each station limits the usable audio bandwidth
to the range 100 Hz to 4.5 kHz.
(It may not be apparent why this maximum frequency isn't twice as high,
that is 9 kHz. The reason is buried in mathematics that will become more
apparent when you study telecommunications at university!)

38 Telecommunications engineering
 As we saw previously, this limited bandwidth results in low-fidelity
sound that does not reproduce music particularly well, but is still
quite satisfactory for speech.
Reception range limits vary from 100 km to 1000's of km (the latter
in ideal conditions such as on a clear night).
Transmitting antennae are generally omnidirectional that is, they
transmit signals in all directions equally. Some AM broadcast
transmitters do have some directionality this is done to broadcast
most of the signal power to areas of highest populations, and to
avoid wasteful broadcasts over unpopulated areas. Directional
broadcasting is achieved by having multiple antennae for AM
broadcasting this is usually two antennae, located perhaps 50 metres
to 100 metres apart.
Figure 5.25 shows a directional antenna used in the Newcastle area.
Note the two towers used. (The two antennae are actually vertical
the apparent lean on the towers is caused by the camera lens!)
Receiving antennae (most often inside the radio receiver) are usually
quite insensitive to direction.

Figure 5.25 AM antenna comprised of two towers to offer some degree

of control of signal transmission direction

FM Broadcasting
The FM broadcast band in Australia extends from 88108 MHz.
The higher frequencies used by FM broadcasting in comparison to
AM broadcasting result in shorter wavelengths, and hence an

Part 5: Electricity/electronics in telecommunications engineering 39

 increased susceptibility to interference from solid objects. You may
have noticed a tendency for FM stations to drop out (or become
unclear) when driving around in a car. This occurs because objects
(buildings, hills, trees) block the direct line between transmitter and
receiver from time to time.
The FM band is divided into separate sub-bands (or frequency
slots) for each radio station. Each frequency slot has a bandwidth
of 200 kHz, and can accommodate an audio soundtrack of 50 Hz to
15 kHz.
This wider range of audio frequencies provides a higher fidelity
sound than is obtained from AM broadcasts.
The channel capacity of an FM broadcast link is greater than for an
AM link due to two factors:
1 The SNR of FM is greater than for AM (assuming equal
amounts of noise power) because the FM waveform is always at
the maximum amplitude, whereas the amplitude of an AM
signal is variable.
2 The bandwidth of the FM broadcast link is 200 kHz compared
with the 9 kHz bandwidth of the AM link.
Transmitting antennae are usually omnidirectional. Receiving
antennae are moderately directional (more so than their AM
counterparts) reception can often be improved by adjusting the
aerial.
Television broadcasting
These systems operate in the 45230 MHz (for VHF) and 520820
MHz (for UHF) bands. The range of reception varies from several
kilometres (in hilly terrain) to hundreds of kilometres (in flat
terrain).
Television broadcasting differs from radio broadcasting most
noticeably in the type of receiving antennae required. Television
receiving antenna are highly directional it is often difficult to get
any picture at all unless your aerial has been tuned to the correct
direction.

40 Telecommunications engineering
 Figure 5.26 Television receiving antenna this antenna is highly directional,
and must be pointed towards the signal source for best results

Mobile communications
These include air-to-air and air-to-ground, marine and terrestrial
mobile radio. All are full-duplex allowing communication in both
directions. Nondirectional antennae are most often used to maintain
useful performance for the system while the vehicle orientation
changes. A broad range of frequencies are used including MF, VHF
and UHF ranges. Mobile telephones are quickly becoming the
dominant example of this type of link.

Figure 5.27 Two way radio used for mobile communications

Navigation systems
Airborne and coastal navigation systems use a variety of radio
beacons to determine position. A broad range of frequencies are
used including VLF, LF, VHF and UHF ranges. These systems are
rapidly being superceded by global positioning systems (GPS)
technologies.

Part 5: Electricity/electronics in telecommunications engineering 41

 Microwave
The term microwave is generally used to refer to highly directional
signals in the SHF and EHF ranges (240 GHz). At these frequencies,
the electromagnetic waves have wavelengths of metres down to
centimetres, and hence can be focussed into narrow beams using
parabolic dishes. (Lower frequencies are much harder to focus because
their longer wavelengths require impractically large dishes.)

The short wavelengths also result in susceptibility to adverse weather

conditions: at frequencies above 10 GHz the relative size of rain droplets
is sufficient to cause signal degradation.

Microwave links are used both for full-duplex point-to-point

communications and for half-duplex one-to-many transmissions. Both
applications require line-of-sight between transmitter and receiver.

The full-duplex point-to-point links are usually between towers located

on prominent landmarks. The dishes at either end require precise
alignment to ensure maximum signal power (and hence channel
capacity). Applications of such links include high volume digital
telephony and data transmissions.

The half-duplex links are most often used for delivery of (pay-)
television. In these applications a transmitting tower broadcasts a semi-
focussed beam across a region. Receiving dishes are aligned towards the
transmitting tower. Such systems offer an attractive (economical)
alternative to cable television which requires expensive cable roll-out
to connect all subscribers.

42 Telecommunications engineering
 Figure 5.28 Microwave dishes used for point-to-point transmissions mounted
high on a telecommunications tower the covers over the dishes
are in place to prevent birds and insects from nesting in the focal
point of the parabolic dish

Satellite communications
While satellite communications are often thought to be a specialised form
of telecommunications, they are in fact simply a microwave link that uses
an orbiting tower to extend the line-of-sight.

The satellites may be geostationary, meaning that they appear stationary

above the earth (they in fact orbit the earth at the same rate that the earth
spins on its axis), or they may be in low earth orbits meaning that they
move across the sky relative to the earth.

Geostationary satellites are further away from the earth than orbiting
satellites meaning that their transmission delays are longer. On the other
hand, it is possible to point a fixed satellite dish at a geostationary
satellite and maintain good reception, whereas a low earth orbiting
satellite needs to be tracked across the sky.

The satellite receives the land-to-space (up-link) signal, reconstructs the

signal to eliminate accumulated noise, and then retransmits the signal to
earth (downlink) using a different frequency.

Part 5: Electricity/electronics in telecommunications engineering 43

 If the same frequency was used in both uplink and downlink, the two
signals would interfere with each other. For this reason, satellite links
are characterised by having separate uplink and downlink frequencies.

Frequencies used for satellite communications are a subset of those used

for terrestrial microwave. Useful frequencies are bounded at the lower
end by land based sources of interference that become too prominent.
Above 10 GHz the earth's atmosphere tends to significantly attenuate the
microwave signals.

Satellite systems can be used to provide one-to-one or one-to-many

communications. Figure 5.29 illustrates both situations.

Point to point
satellite link

Up link Down link

Satellite
broadcasting

Figure 5.29 Satellites used to provide point to point and broadcast facilities

Infrared
Infrared signals are normally defined to be those just below the visible
spectrum. Typical wavelengths used are 880 to 950 nm (nanometres).
Transmission is by line-of-sight, and useful range is up to 10 metres.
Most applications use a simple half-duplex system. Applications
requiring bidirectional data transmission usually achieve this by using
two half-duplex systems.

44 Telecommunications engineering
 The relatively low cost of infrared transmitters and receivers has
popularised their use in many and varied situations. Remote controllers
for television, video and audio systems, cordless connections between
computers and peripherals and security applications are now relatively
common.

Figure 5.30 A common application of infrared transmission in this case a

remote controller from an audio system

Turn to the exercise section and complete exercise 5.8.

Part 5: Electricity/electronics in telecommunications engineering 45

 Evaluating telecommunications systems
In the preceding work we have learned about a number of
telecommunications principles, including:
analogue and digital signals
the effects of bandwidth and signal to noise ratio on channel capacity
images for transmitting information
modulation techniques (to enhance signal propagation)
transmission media, including guided and unguided forms.

We can now look at any telecommunications system and evaluate them

in terms of the above parameters. In this way we appreciate why some
systems work better than others, why some systems cost more than
others, and how telecommunications systems might evolve in the future.

Analogue and digital data and systems

We have seen analogue and digital signals, and have also seen analogue
and digital transmission systems. There are four combinations:
analogue data over analogue links
analogue data over digital links
digital data over analogue links
digital data over digital links.

Table 5.5 summaries the various combinations, and gives examples of

each.

Analogue transmission Digital transmission

Analogue Data Signals are sent at baseband Sample and quantise

or modulated to higher analogue signal to form
frequency using AM or FM. digital data. Example:
Example: radio and television digital mobile telephone.
broadcasting.

Digital Data Use Shift Keying methods Data formed into packets
(ASK, FSK, PSK) to modulate and sent using digital
an analogue carrier. Example: signalling. Example: local
computer modem connected to area computer networks
telephone system. (LANs).

Table 5.5 Combinations of analogue and digital data and transmission

46 Telecommunications engineering
 Describing a telecommunications system
Modern telecommunications systems are very complex. Invariably, a
particular application (such as a mobile telephone, a fax machine or
television transmission) will consist of many subsystems. As such, it is
difficult to answer simplistic questions such as Describe how a mobile
telephone works. To answer this completely and correctly, we would
need to identify every link in the system, and describe each according to
its key parameters.

Another approach to describing telecommunications applications is to

identify what characteristic or characteristics are unique to the particular
application and differentiate it from other similar or related systems.

For example, a mobile telephone shares many characteristics with a fixed

telephone: they are both used to convey analogue signals in the range
from 300 Hz to 3 500 Hz from one handset to another.

Mobile telephony differs from fixed telephony in that a mobile phone

uses a modulated carrier at microwave frequencies across an unguided
medium to link it to the fixed telephony network, whereas a fixed
telephone uses a twisted pair cable at baseband frequencies to link it with
the fixed telephone network.

The fact that most mobile telephones convert the analogue voice signal to
a digital signal before transmission does not necessarily distinguish
mobile telephones from fixed telephones: a fixed telephone could also
convert its analogue input into a digital signal for communication with
the network.

To assist with understanding and categorising telecommunications

systems, it is sometimes insightful to ask the following questions:
1 Is the information speech/music, text/numerics, images and/or
video?
2 Is the information analogue or digital?
3 Is the transmission from point-to-point, or is it broadcast to many?
4 Is the device in question part of a much larger and commonly used
system?
In some cases we can investigate the technicalities more closely.
5 How many different links are used between sending and receiving
ends?
For each link:
Is the link between sending and receiving ends analogue or digital?
Is the link a guided or unguided medium?

Part 5: Electricity/electronics in telecommunications engineering 47

 What medium is used?
Is modulation used to propagate the signal?

The specific answers to these latter questions are often not obvious to the
casual observer. Only an engineer or technician involved in that
particular industry would be able to respond with certainty.

Let us try an example.

Facsimile machine

Figure 5.31 Facsimile machine that transmits digitised images over a telephone
line

1 Is the information speech/music, text/numerics, images and/or

video?
A facsimile machine is used to transmit text and images from a
printed page. The text, however, is treated as though it were an
image, and is not transmitted as a series of characters or symbols.
So to be correct, we should say that only images are sent.
2 Is the information analogue or digital?
The images are treated as continuous or analogue signals. The fax
machine converts the analogue image into digital data using
sampling and quantisation. The sampling is at around 150 dpi, and
the quantisation is monochrome (black and white).
3 Is the transmission from point-to-point, or is it broadcast to many?
The transmission is point-to-point. (A mass faxing to many
recipients is actually handled as many separate fax transmissions.)
4 Is the device in question part of a much larger and commonly used
system?
A facsimile machine is part of a much larger telephone system. The
image is digitised, and audio tones are used to represent the digital

48 Telecommunications engineering
 information. These tones are then handled by the telephone system
as if it were a telephone call.
5 How many different links are used between sending and receiving
ends?
At least several, often many. There is a link from the facsimile
machine to the exchange, from exchange to exchange, and then from
exchange to receiver. Between exchanges there could be additional
links.
Is the link between sending and receiving ends analogue or digital?
The link to the exchange is analogue. Links between exchanges
are most often digital.
Is the link a guided or unguided medium? What medium is
used?
The link from machine to exchange is guided via twisted pair
cable. Between exchanges the link is likely to be by optical
fibres or microwave links.
Is modulation used to propagate the signal?
The link to the exchange uses audio tones to represent digital
data. A combination of Amplitude and Phase Shift Keying is
used. The optical fibre also uses Amplitude and Phase Shift
Keying to modulate a light source. The microwave link uses a
combination of Amplitude and Phase Shift Keying to modulate
a microwave carrier.

Colour television

Figure 5.32 Colour television used to receive broadcast video and sound signals

1 Is the information speech/music, text/numerics, images and/or

video?
The information received is video and sound. The video is in RGB
colour.
2 Is the information analogue or digital?

Part 5: Electricity/electronics in telecommunications engineering 49

 Both the vision and sound are analogue signals (though soon to be
replaced by digital television through the next decade!).
3 Is the transmission from point-to-point, or is it broadcast to many?
The television signal (video and sound) is broadcast to many
receivers.
4 Is the device in question part of a much larger and commonly used
system?
The television broadcast network is virtually stand-alone. There is a
small market for teletext information systems that are piggy backed
onto the television broadcasts. Television receivers are usually used
for the sole purpose of receiving television broadcasts.
5 How many different links are used between sending and receiving
ends?
There are generally two or three links in the transmission system:
from studio to broadcast transmitter, or
from studio to relay tower (to relay tower ) to transmitter, and
from transmitter to receiving antenna.
We will consider only the final transmitter to receiver link.
Is the link between sending and receiving ends analogue or
digital?
The transmitter broadcasts two analogue signals to receivers:
one for vision, and a separate signal for sound.
Is the link a guided or unguided medium?
The transmitter to receiver is via unguided VHF or UHF
transmissions.
What medium is used?
The signals are broadcast through the air.
Is modulation used to propagate the signal?
The broadcast signal uses Amplitude Modulation for the vision,
and Frequency Modulation for sound.

50 Telecommunications engineering
 Internet browsing via a modem

Figure 5.33 Modem used to connect a digital computer to analogue telephone lines

1 Is the information speech/music, text/numerics, images and/or

video?
Internet browsers access all types of information.
2 Is the information analogue or digital?
All of the sources of information are digital, or are digitised to be
distributed and interpreted by computers. The original sources of
information are a mixture of analogue (music, voice, images) and
digital (text, numerics).
3 Is the transmission from point-to-point, or is it broadcast to many?
The communication links are point-to-point between the web server
and the browser.
4 Is the device in question part of a much larger and commonly used
system?
The modem invariably uses the telephone system to connect the
browser to the service provider. The service provider is connected to
the computer network by high speed shared or dedicated telephone
lines. The computer network is a very large interconnection of
web servers spread across the world.
5 How many different links are used between sending and receiving
ends?
Many! Indeed it is this aspect that characterises the internet. Its
flexibility, size and scope is a function of the large number of
interconnected machines. It is likely that there is no other
application of telecommunications that uses more and varied links to
achieve its purpose!
For the purposes of illustration, let us consider only the modem
connection to the telephone network.
Is the link between sending and receiving ends analogue or digital?
The link between the modem and the telephone system is an
analogue connection, designed originally for voice
communication (300 Hz to 3 500 Hz).

Part 5: Electricity/electronics in telecommunications engineering 51

 Is the link a guided or unguided medium? What medium is used?
The link is a (guided) twisted pair.
Is modulation used to propagate the signal?
The data in and out of the computer is digital (binary). The modem
is used to interface the digital computer to the analogue line.
The term modem is actually an abbreviation of modulator
demodulator. Its function is to encode the digital data from the
computer into audio tones for transmission across the telephone
network.
A combination of amplitude and phase shift keying is used. By
using combinations of amplitude and phase modulation, we
effectively create a multilevel signal (like that shown in figure
5.2) that can transmit two or more bits of information at a time.
The precise format of the modulation used is dependent on the
modem standard being used. For example, V.34 and V.90 use
different levels and combinations of amplitude and phase shift
keying schemes to represent data.

While we are talking about modems, we might ask "What causes the
'beeping' that is heard when a modem first connects to the service
provider"?

The modem connects to the service provider by dialing the provider's

telephone number. In this situation, the modem is behaving as though it
were a telephone.

The various tones that are heard are used to signal the keys (numbers) on
the dialing keypad. Each key is represented by the combination of two
audible tones. Table 5.6 sets out the tones used for each symbol.

Tone 1209 Hz 1336 Hz 1477 Hz

697 Hz 1 2 3

770 Hz 4 5 6

852 Hz 7 8 9

941 Hz * 0 #

Table 5.6 Tones used in tone dialed telephone systems

When a particular key is pressed, the corresponding two tones are sent
down the line. Since the two tones are at different frequencies, we can

52 Telecommunications engineering
 distinguish between them at the receiving end, even though they are
transmitted concurrently.

You might also hear the same tones when you use an ordinary fixed
telephone handpiece. The system is called DTMF, or Dual Tone
Multiple Frequency dialing.

Figure 5.34 Telephone handset that uses Dual Tone Multiple Frequency (DTMF) dialing,
giving a series of 'beeps' at various frequencies as it dials the numbers

Turn to the exercise section and complete exercise 5.9.

Part 5: Electricity/electronics in telecommunications engineering 53

54 Telecommunications engineering
 Exercises

Exercise 5.1

Describe the two main differences between analogue and digital signals.
1 _______________________________________________________
_______________________________________________________
2 _______________________________________________________
_______________________________________________________

Exercise 5.2

Explain why a radio transmitter for an AM broadcast station is much

larger than the antenna on a mobile telephone.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________

Exercise 5.3

Why does digital signaling usually perform better than analogue

signaling in a noisy communications channel?
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________

Part 5: Electricity/electronics in telecommunications engineering 55

 Exercise 5.4

Give four reasons why telecommunications systems are increasingly

becoming digital rather than analogue.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Exercise 5.5

Explain why you would either (a) double the bandwidth, or (b) double
the signal amplitude if you had money to spend to improve the channel
capacity of a telecommunications link.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Exercise 5.6
a Give a reason why Amplitude Modulation is preferable to Frequency
Modulation for radio broadcasting?
_______________________________________________________
_______________________________________________________
b Give a reason why Frequency Modulation is preferable to Amplitude
Modulation for radio broadcasting?
_______________________________________________________
_______________________________________________________

56 Telecommunications engineering
 Exercise 5.7

Describe three ways in which digital information can be represented as

an analogue signal.
1 _______________________________________________________
2 _______________________________________________________
3 _______________________________________________________

Exercise 5.8

State one advantage in favour of using each of the following media:

a twisted pair cable
___________________________________________________________
b coaxial cable
___________________________________________________________
c optical fibre
___________________________________________________________
d AM radio
___________________________________________________________
e microwave links
___________________________________________________________
f satellite links.

___________________________________________________________

Part 5: Electricity/electronics in telecommunications engineering 57

 Exercise 5.9

Select the alternative a, b, c, or d that best completes the statement.

Circle the letter.

1 An analogue signal:
a is one that has an infinite number of possible values of amplitude
b can be sampled at any instant in time
c can be represented by a continuous graph of amplitude plotted
against time
d all of the above.

2 A digital signal:
a is what we hear from a digital mobile telephone
b has only two possible amplitudes
c should only be evaluated at the correct instants in time
d is a gesture made by raising any number of fingers.

3 A multilevel signal:
a has only two possible values, but at any voltages
b can represent two or more bits of information in one signaling interval
c is obtained from a binary signal by transmitting bits more quickly
d is the result of faulty equipment.

4 A binary digital signal generally occupies:

a less bandwidth than a single sinusoidal signal
b more bandwidth than a single sinusoidal signal
c the same bandwidth as a single sinusoidal signal
d the house next door to the mad scientist with the yellow parrot.

5 Electrical noise is present in all electrical circuits, but:

a we can ignore it
b we can turn it down
c we can overcome its effects in any circuit
d we can overcome its effects in some instances.

6 The bandwidth of a telecommunications link:

a tells us how large the microwave dishes have to be
b describes the range of frequencies that it can propagate
c increases with antenna height
d is generally insignificant in telecommunications engineering.

58 Telecommunications engineering
 7 The capacity of a telecommunications link is dependent on:
a the number of computers connected to it
b the height of the towers supporting the microwave dishes
c whether it transmits analogue or digital data
d the bandwidth and signal to noise ratio.

8 The dynamic range of a signal is:

a the difference between the minimum and maximum amplitudes
b the distance it can travel in free space
c the speed it can travel in an optical fibre
d all of the above.

9 The size of a stored digital image is:

a determined by the resolution (in dpi) and the number of pixels used
b determined by the number of pixels and the number of colours used
c determined by the resolution (in dpi) and the number of colours used
d the size of the computer's hard disc.

10 Modulation involves:
a sampling and quantisation
b using different frequencies for radio stations
c eliminating noise
d varying a parameter of a carrier wave according to a message
signal.

11 Modulation is used to:

a increase the bandwidth of a signal
b increase the amplitude of a signal
c increase the signal to noise ratio of a signal
d allow the modulated signal to propagate more efficiently
through a given medium.

12 Amplitude modulation:
a has a lesser signal to noise ratio than Frequency Modulation
b is relatively cheap to generate and decode
c is quite suitable for voice communications
d all of the above.

Part 5: Electricity/electronics in telecommunications engineering 59

 13 Frequency modulation:
a varies the frequency of the carrier in proportion to the message
signal's amplitude
b varies the frequency of the carrier in proportion to the message
signal's frequency
c varies the amplitude of the carrier in proportion to the message
signal's frequency
d varies the amplitude of the carrier in proportion to the message
signal's amplitude.

14 The electromagnetic spectrum:

a describes the range of frequencies used by all types of
electromagnetic communications equipment
b is a common resource that anyone can use as they please
c is a telecommunications system that was built by foreign
interests
d is limited by the range of channels on a television receiver.

15 Twisted pair cables:

a are used to scramble digital signals so that they can't be
intercepted by a third party
b result from frequent wiring and rewiring of telephone exchanges
c are a low cost guided medium used for telephone and low
speed digital communications
d are a suitable replacement for optical fibres in high speed
applications.

16 Coaxial cables:
a have a wider bandwidth than optical fibres
b are constructed from a central glass fibre surrounded by a metal
foil shield
c have a wider bandwidth than twisted pair cables
d can carry larger signal amplitudes than twisted pair cables.

17 The extremely wide bandwidth of optical fibres is a result of:

a using light instead of electrical current for signaling
b the very short wavelength of visible light
c having very good electrical noise rejection
d a fundamental physical property of the medium.

60 Telecommunications engineering
 18 The guided medium with the highest channel capacity is:
a mains wiring
b twisted pair cabling
c coaxial cabling
d optical fibres.

19 Unguided media:
a are journalists who do as they like
b is the term used to describe telecommunication links that are not
physically connected
c is the term used to describe telecommunication links that use
microwave links
d is another term for radio communications.

20 The usable range of an unguided medium transmission depends on:

a the number and size of obstacles in the path
b the power of the transmission signal
c the amount of noise in the channel
d all of the above.

21 FM radio broadcasts have a superior sound quality because:

a they are a newer technology
b they don't broadcast advertisements
c they have a wider bandwidth and better signal to noise ratios
d they use higher frequencies and shorter wavelengths.

22 Television receiving antenna are an unusual shape because:

a they are essentially a structural component for a house roof
b they are designed to receive frequency modulated signals
c they are fashionable
d they are highly directional to increase signal to noise ratios.

23 A microwave signal is one that:

a only works in conjunction with amplitude and Phase Shift Keying
b has a wavelength that allows beams to be shaped by parabolic dishes
c can only be used between transmitters located on tall towers
d only works in fine weather.

Part 5: Electricity/electronics in telecommunications engineering 61

 24 Satellite communications are:
a a unique type of telecommunications link that uses special
signaling methods
b expensive because of the distance the signals have to travel
c achieved by reflecting a signal off an orbiting dish
d is really the same as microwave signaling, but with receivers
and transmitters located in space.

62 Telecommunications engineering
 Progress check

In this part you examined the principles that underpin many of the
telecommunications technologies currently in use.
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.

Agree well done

Uncertain

Disagree
Disagree revise your work

Agree

Uncertain contact your teacher

I have learnt about:

telecommunications
analogue and digital systems, modulation,
demodulation, radio transmission (AM, FM),
television transmission (B/W, colour), telephony
(fixed and mobile), transmission media (cable,
microwave, fibre-optics)
satellite communication systems, geostations.

I have learnt to:

describe the basic concepts and applications of
modulation and transmission systems in
telecommunications
distinguish the communication bands in the
electromagnetic spectrum
contrast the differences in transmission media
describe the basic principles of satellite communication
systems.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

In the next part you will continue to develop skills in representing objects
using freehand and technical drawing, and be given opportunity to
develop CAD skills, applying AS1100 drawing standards where
appropriate.

Part 5: Electricity/electronics in telecommunications engineering 63

64 Telecommunications engineering
 Exercise cover sheet

Exercises 5.1 to 5.10 Name: _______________________________

Have you have completed the following exercises?

Exercise 5.1
Exercise 5.2
Exercise 5.3
Exercise 5.4
Exercise 5.5
Exercise 5.6
Exercise 5.7
Exercise 5.8
Exercise 5.9

Locate and complete any outstanding exercises then attach your

responses to this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your
responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learners Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.

Part 5: Electricity/electronics in telecommunications engineering 65

Telecommunications engineering

Part 6: Telecommunications engineering

communications
 Part 6 contents

Introduction ..........................................................................................2

What will you learn?...................................................................2

Communication tools of the engineer..............................................3

Teamwork .................................................................................4

Orthogonal drawing....................................................................5

CAD advantages .......................................................................6

Electronic/electrical component representation ............................6

Technical representation in detail................................................9

Exercises............................................................................................15

Progress check .................................................................................35

Exercise cover sheet........................................................................37

Bibliography.......................................................................................39

Module evaluation.............................................................................43

Part 6: Telecommunications engineering communications 1

 Introduction

This communication part of the module will further consolidate and review the
communications content presented to you in earlier modules. You will
continue to develop your skills in representing objects using technical drawing
and freehand communication.

You will be given the opportunity to develop your CAD skills, and be asked to
consider the relevance of communicating technical information as it might
relate to an engineer working in the telecommunication area.

You will be expected to apply AS1100 drawing standards where appropriate.

You will be expected to complete several exercises in this module part in order
to develop and demonstrate your communication skills.

What will you learn?

You will learn about:
freehand and technical drawing, pictorial and dimensioned orthogonal
drawing
Australian standards AS1100
computer graphics, computer assisted drawing (CAD)
collaborative work practices.

You will learn to:

produce orthogonal drawings applying appropriate Australian Standards
(AS1100)
apply dimensions to drawings to AS1100 standard
justify graphics as a communication tool for telecommunications
engineering
appreciate the value of collaborative working.

Extract from Stage 6 Engineering Studies Syllabus Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

2 Telecommunications engineering
 Communication tools of the engineer

You might recall the notes on communication technical drawing. An engineer

working in telecommunications, like all engineers, will be expected to
communicate technical information accurately. The importance of accuracy in
communication is critical.

So what tools does the engineer have?

You might consider the traditional tools such as drawing equipment, but there
are a new and emerging array of alternatives. In addition to the hardware and
software tools you may have thought about, other forms of tools might be
considered. The Australian Standards provide a framework to be used as a tool
for accurate communication. Without that tool, mis-communication would be a
regular occurrence and could easily lead to disaster. The written language and
verbal communication are also essential. Engineers are required to write
engineering reports and make presentations.

List the tools available for the engineer to use in order to communicate.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________

Did you answer?

Some of the tools incude:
computer links email, video
telephone, fax, video
conferences, meetings
standards
CAD software.

Part 6: Telecommunications engineering communications 3

 Team work
All engineers will be required to work collaboratively. Perhaps during the early
1900s some gifted engineers might have completed projects as individuals. In
the engineering world we live in, this would now be a rare event. There is
much more likely to be a structure in place for a variety of technical groups to
work collaboratively on any project. A team approach is a proven technique for
attaining the optimum results. In the telecommunication field, it is difficult to
imagine one person developing a product or system in isolation. While
individuals may well have the inspirational idea, or provide a key
breakthrough, it will require a team to turn that idea into a commercial
application.

Consider the development of one telecommunication product.

Make a list of the technical skills that the collaborative team might have
needed during the development of the product. The list might start with a
great idea.

A great idea an inspiration creative thinking

Then:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________

Did you answer?

Some of the technical skills required may include:
electrical engineering
computer engineering
mechanical engineering
production engineering
technical drafting
marketing and sales.

4 Telecommunications engineering
 Orthogonal drawing
At this stage of the course you will have read about many AS1100 standards.
You would have had the opportunity to test your own skills at applying these
standards. You would be aware of the importance of these standards in all
engineering fields.

The standards are applied in technical drawings completed using drawing

instruments or when using a CAD program. Software drawing programs do not
necessarily apply drawing standards just as drawing instruments do not apply
them. The CAD program is a drawing tool. The user must have acquired
technical drawing knowledge if a standards drawing is to be produced. It is
important to note that drawing standards do not stop when freehand technique
is used. While not all standards can be applied accurately with freehand
drawing, the concepts should always be applied if accurate communication is
to occur.

Figure 6.1 Instrument and freehand orthogonal drawing

Part 6: Telecommunications engineering communications 5

 CAD advantages
The engineer working on a design concept is very likely to begin the process
with freehand sketches. These freehand sketches are likely to be refined several
times before an instrument or CAD drawing is produced. The main advantage
of all CAD drawings is that they can be continually modified without the need
to start the drawing over again. CAD drawing is not necessarily faster to do,
the advantage is much more likely to be the ease of modification and alteration.

The CAD drawing is also flexible in that versions can be produced specifically
targeted for various needs. For instance, the electrical/electronic content can be
removed (not displayed) when presenting specification drawings to the
polymer manufacturer involved in moulding the case of the product.

Another consideration is the ease of information transfer using CAD. Because

the information is stored digitally, it can be transferred electronically. This not
only allows nearly instant communication amongst the team in the office, it
allows information to be transferred immediately throughout the computer
network around the world.

With CAD software technology developing rapidly, it has become common

place for objects drawn in 2 dimensional orthogonal projection, to be
transformed into 3 dimensional images. The 3 dimensional image is able to
have its surfaces automatically rendered to selected surface textures. The object
can be viewed from any direction and rotated as a moving picture. Walk
through features in CAD programs allows the spectator to have a real three
dimensional view of the object even from inside commonly used on house
plan designs or for technical presentations.

Now turn to the exercise sheet and complete exercise 6.1.

Electronic/electrical component
representation
In order to communicate electrical circuitry, electrical and electronic engineers
will need to be able to read electrical circuit diagrams and design electrical
circuits. You might be aware of basic circuitry diagrams from studying house
plans or from looking at electronic magazines.

What communication skills are required for electrical drawings?

6 Telecommunications engineering
 Like all technical drawing, there are specific standards that apply when
drawing circuits. The list of symbols used to represent components in the
circuit appear to be endless. However, there is no need for you to be familiar
with the vast array of symbols. Concentrate on being able to recognise the
more common circuit symbols.

Because the field of electrical control is so vast, engineers specialise.

Representing the electrical circuit in a building will be significantly different
from representing the circuit components used in an electronic control device.
There are symbols used when designing the larger system of control devices
(switches, cabling, lighting, power outlets, etc.), and there are symbols used
specifically when designing electronic components that are attached to a
printed circuit board (transistors, resistors, capacitors, etc.).

You should develop an elementary knowledge of identifying both electronic

circuit board components and electrical system components.

A selection of electronic symbols are shown in the following table.

Component Symbol

Resistor

Capacitor (non
polarised)

Capacitor (polarised)

Battery ....
+

Diode +

Integrated circuit 1 4
2 3

Transistor C
B
E

Light Emitting Diode

Part 6: Telecommunications engineering communications 7

 A selection of electrical symbols is shown in the following table.

Component Symbol

Switch

Light

Power outlet

Transformer

Earth
or

Fuse

Motor M or M o
~

Now turn to the exercise sheet and complete exercise 6.2.

You are required to freehand draw the appropriate symbol for each of the
components indicated.

8 Telecommunications engineering
 Technical representation of the detail
You may recall the following topics from past modules:

Civil structures
Developments
In engineering, the design of sheetmetal objects is done using flat surfaces.
The flat shapes obtained are folded to form the required object. The
method used to create the correct flat shape include parallel development
(for simple shapes), radial developments (for cones or pyramids) and
dividing the shape into triangular segments (triangulation) when
developing transition pieces.
True length of lines
To develop objects to specified sizes, developments must use true sizes
(scaled) rather than apparent sizes which are often created when objects
are drawn using orthogonal projection. True lengths are determined using
several methods, including the:
rotation method
auxiliary plane method
offset method.
Each of these methods relies on the fact that a line will be seen as a true
length if it is projected from a line that is parallel to the projection plane.
Transition pieces
The common application of transition pieces is in ventilation ducts.
Connection segments are often required to join different shaped ducts. The
connection segments are called transition pieces.
Representing threads, nuts and bolts
Drawing, or representing, threaded components requires many AS 1100
standards to be applied. Representing threaded devices is critical because
drawing the actual shape of the thread would be time consuming.
Applying AS 1100 standards accurately is essential.

Part 6: Telecommunications engineering communications 9

 Sectioning
Viewing the internal shape of objects is regularly required in order to gain
a full understanding of how the components are assembled or for
manufacturing detail. Rather than show hidden detail construction, the
object is viewed as if cut. Many AS 1100 rules need to be applied when
showing objects in section.

Personal and public transport

Drawing sheet borders, title blocks and 3rd angle logo
Students often underestimate the significance of these sheet details. The
technical drawer needs to communicate accurately. This is only possible if
sheet details are displayed. There are AS 1100 standards to be applied for
consistency.
AS1100 symbols
The use of clear and unambiguous symbols has an advantage over written
comments. Symbols reduce drawing time and allow the drawing to cross
international borders. A few of the symbols include:
3rd angle logo
square holes
depth of holes
diameter of holes
countersunk holes
counterbore holes
spotfacing
spherical radius
chamfered corners
springs
knurls
flat surfaces
breaks.
Auxiliary views
Often when a single orthogonal view is drawn, the location and shape of
some details need to be determined by projection from another view. The
view drawn in order to determine these details is called an auxiliary view.
The auxiliary view does not need to be a complete orthogonal view, but

10 Telecommunications engineering
 rather, construction can be limited in order to supply only the required
information.
Freehand drawing
Engineers are required to convey information quickly but with accuracy.
An important skill is the ability to produce freehand drawings. Freehand
drawings need to use all the AS 1100 concepts. Without these standards
the drawing will be less able to communicate accurate details. While some
AS 1100 standards are difficult to apply using freehand, the fundamental
concepts should always be applied.

Lifting Devices
Representing repeat features
When a component contains regular repeating features such as holes or
slots, the AS 1100 standards allow these repeat features to be shown as full
outline or alternatively, by a conventional representation. Examples
include drilled holes at a set distance from a central hole. Rather than draw
a series of holes, one hole is drawn, then the details of the remaining holes
are indicated using symbols. Pitch circle diameter (PCD) refers to the
diameter that the hole centres are located from the centre point.
Material lists
Material lists or parts lists should be used when several components are
detailed in one drawing, or a number of components are shown in one
assembly drawing. The material list should be positioned near the sheet
title block.
Itemising
Often a component on an assembly drawing is assigned an item number.
The number is used to identify the component and is referenced to the
material list. Leaders (lines) are continuous thin dark lines drawn from the
item number to the component.
Square threads
Where screw threads are used to transmit large forces, such as in lifting
devices, square thread is used rather then the more common v-thread. To
differentiate a square thread from a v-thread a section of the detail view is
drawn to illustrate the thread shape.
Tangency
Tangency refers to the joining of lines. These lines can be the edge of a
circle or an arc meeting a straight line, or can be arc to arc, or circle to
circle. Construction techniques are required to ensure accurate tangency.

Part 6: Telecommunications engineering communications 11

 Aeronautical engineering
Drawing scales
Drawing scales are required in order to accurately draw objects that are too
large to represent full size, and for objects that are too small to draw
accurately at actual size. Rather than have endless variation between
drawings, a series of preferred scales are used. Enlarging scales are written
10:1 etc. Reduction scales are written 1:10 etc. A simple way of
determining if a scale is an enlarging or reducing scale is to consider the :
sign as a / sign. Thus, a 1:10 scale can be thought of as a 1/10 th size
drawing.
Selection of views
When selecting the views required, the drawer should aim to:
reduce the number of views required to give a full shape description
avoid repetition of detail or views
avoid hidden detail.
Partial and auxiliary views
Partial views are used where full shape views do not provide good shape
description. They apply where a component has an inclined face and are
often used in conjunction with an auxiliary view.
Symmetrical parts
When components or parts are symmetrical, time can be saved, without
loss of accuracy, by drawing half shapes or patterns. AS 1100 standards
are applied to indicate lines of symmetry.

It would be advisable to review each of the parts in each module, and refresh
your memory of the details. This knowledge will need to be recalled in order to
complete the exercises that follow.

Collecting the data for exercise 6.3

Prepare yourself with a tape measure, paper and a few sharp pencils.

Find a public telephone. Make as many in the field sketches of the

telephone, and the telephone booth, as you can. Take as many
measurements as you can. You will need the dimensions of the telephone
booth, concrete footing, height of telephone above the floor level. Before
you begin to collect this information, turn to exercise 6.3 to read the
instructions.

12 Telecommunications engineering
 Figure 6.2 Telephone booth

Now turn to the exercise sheet and complete exercises 6.3 to 6.6.

Part 6: Telecommunications engineering communications 13

14 Telecommunications engineering
 Exercises

Exercise 6.1

This exercise requires a CAD drawing. This CAD drawing will be a very
simple icon representation of a telephone booth. You should allocate
approximately 20 minutes for this exercise. This icon should be a
suitable simple and clear design for inclusion on a site map.

There is no requirement for a detailed technical drawing, you need to

represent the telephone booth without detail. The icon should be easily
read when reproduced within a 20mm by 20mm square.

An enlarged image 100 x 100 mm, and a 20 x 20 mm image, should be

printed off and attached to the spaces provided on the next page.

Part 6: Telecommunications engineering communications 15

 Telephone icon enlarged view (100 mm x 100 mm)

Telephone icon standard view (20 mm x 20 mm)

16 Telecommunications engineering
 Exercise 6.2

This exercise requires the drawing of several electronic component symbols.

These symbols should be drawn freehand in the appropriate positions indicated
on the following circuit diagram.
resistor diode

resistor

transistor

transistor resistor

capacitor

capacitor

transistor
+
LED
battery
Figure 6.3 Electronic circuit requiring component symbols

Part 6: Telecommunications engineering communications 17

 Exercise 6.3

This exercise requires a freehand orthogonal front view of the telephone booth
to be drawn. Add general detail and show overall sizes. Although freehand
technique is to be used, apply AS1100 concepts and techniques to the drawing.
This technical drawing should be used to give the viewer overall reference of the
telephone booth design, and be able to be used to identify the location of the
smaller components of the telephone box. Construct a full title block and item
list on this drawing sheet. Show projection angle. Use a scale of 1:10.

Figure 6.4 Telephone booth image 1

18 Telecommunications engineering
 Figure 6.5 Telephone booth image 2 Figure 6.6 Telephone booth image 3

Part 6: Telecommunications engineering communications 19

20 Telecommunications engineering
 Ex 6.3

SCALE 1:10

Part 6: Telecommunications communication Page 21

 Exercise 6.4

From the photographs on this page and the next, draw a three view (left end,
front and right end) freehand orthogonal view that represents the threaded
fixing device shown, using a scale of 2:1. These views will best fit on one
centre, with the drawing sheet orientated in a landscape position.

The bolt is 45 mm long with a thread of M10. All additional sizes to those
provided must be estimated from the photographs. Fully dimension your
drawing, with enough detail to allow for manufacture of the bolt.

Figure 6.7 Threaded fixing device image 1

Figure 6.8 Threaded fixing device image 2

Part 6: Telecommunications engineering communications 23

 Figure 6.9 Threaded fixing device image 3

24 Telecommunications engineering
 Ex 6.4

SCALE 1:1

Part 6: Telecommunications communication Page 25

 Exercise 6.5

From the details provided in the illustrations, draw a freehand pictorial view of
the satellite dish and the supporting structure. Drawing space is provided after
the illustrations. All sizes should be estimated from the illustrations.
Alternatively, if you have access to a satellite dish, you may draw the details of
that dish and its supporting bracket.

Figure 6.10 Satellite dish image 1

Figure 6.11 Satellite dish image 2

Part 6: Telecommunications engineering communications 27

 Figure 6.12 Satellite dish image 3

Figure 6.13 Satellite dish image 4

28 Telecommunications engineering
 Ex 6.5

SCALE 1:1

Part 6: Telecommunications communication Page 29

 Exercise 6.6

Select the most appropriate alternative a, b, c or d that best answers the

question or best completes the statement.

1 When indicating a line of symmetry:

a a thick chain line is used; two short lines are drawn at each end at right
angles to the line of symmetry
b a thin chain line is used; two short lines are drawn at each end at right
angles to the line of symmetry
c a thin chain line is used; the ends of the chain line are thickened, and
two short parallel lines are drawn across the line of symmetry
d a thick chain line is used; the ends of the chain line are thickened, and
two short parallel lines are drawn across the line of symmetry.

2 When selecting views:

a avoid hidden outline
b avoid hidden outline and repetition of views
c avoid hidden outline, repetition of views and have the minimum
number of views that provide full shape description
d avoid hidden outline, repetition of views and have the minimum
number of views that provide full shape description but include a
sectional view.

3 Scaled views are regularly required because:

a objects are never the appropriate size for the paper size
b true sizes do not always allow sufficient detail to be indicated
c to provide full shape description, objects must be drawn larger than
full size
d objects must be drawn at a size that is convenient and appropriate.

4 PCD refers to:

a pitch circle diameter
b partial CAD drawing
c electrical symbols used on PCBs
d the diameter of a thread on a bolt or nut.

5 When dimensioning a technical drawing:

a actual sizes are indicated
b drawn sizes are indicated
c scaled sizes are indicated
d actual sizes are scaled.

Part 6: Telecommunications engineering communications 31

 6 Transition pieces are:
a missing parts between components
b disassembled parts of a development
c developed drawings
d connection segments joining different shaped ducts.

7 A 20 x 20 mm sheetmetal cube, placed in a standard position in an

orthogonal drawing:
a will have edges of apparent length 20 mm in a top view
b will have all parallel edges shown as 20 mm
c will have all edges shown as true lengths
d will have all edges that are parallel to the viewing plane shown as true
lengths.

8 Triangulation is:
a a method of dividing a surface into segments
b finding the location of points
c dividing square surfaces into triangles
d none of the above.

9 Hexagonal nuts and bolt heads should be viewed:

a with three sides shown in the front view
b shown with a spiral cut thread in orthogonal views
c shown with the thread as hidden detail lines
d drawn twice the diameter of the shaft of the bolt.

10 AS 1100 standards use the following letters as symbols:

a SR, S, R, and M
b A/F, S, M and QD
c SR, S, QD and M
d R, SR, A/F and O.

11 AS 1100 rules regarding centre lines state:

a centre lines should extend only a short distance past the feature unless
required for dimensioning
b centre lines should cross one another on a dash part of the line when
they define a centre point
c centre lines are drawn as chain lines
d all of the above.

32 Telecommunications engineering
 12 A detail drawing:
a gives a full size and shape description of the object
b states the material that the object is made
c provides sufficient information for the manufacture of the object
d all of the above.

13 Which of the following lists only contain terms for physical features of
engineering objects?
a radius, collar, web, blind hole, and shoulder
b shaft, taper, boss ,fillet and countersunk
c counterbore, step, flange, thread and spigot
d all three of the lists above.

14 Engineering is about:
a evaluating alternatives and designing the best criteria
b setting criteria and calculating the costs of the best design
c working collaboratively to ensure a consensus is always reached
d determining the best solution based on the criteria.

15 At what stage of the course module work are you at now?

a very close to finished
b ready to review all past work
c ready for the HSC examination
d none of the above
e some of the above.

Part 6: Telecommunications engineering communications 33

34 Telecommunications engineering
 Progress check

During this part you have learned more about the use of drawings in
communicating information and have reviewed the work you have done in
previous modules on drawing to AS1100 standards.
Take a few moments to reflect on your learning then tick the box that best
represents your level of achievement.

Agree well done

Uncertain

Disagree
Disagree revise your work

Agree

Uncertain contact your teacher

I have learnt about:

freehand and technical drawing, pictorial and

dimensioned orthogonal drawing
Australian standards AS1100
computer graphics, computer assisted drawing (CAD)
collaborative work practices.

I have learnt to:

produce orthogonal drawings applying appropriate

Australian Standards (AS1100)
apply dimensions to drawings to AS1100 standard
justify graphics as a communication tool for
telecommunications engineering
appreciate the value of collaborative working.

Extract from Stage 6 Engineering Studies Syllabus, Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

Congratulations! You have completed the module on Telecommunications

engineering.

Part 6: Telecommunications engineering communications 35

36 Telecommunications engineering
 Exercise cover sheet

Exercises 6.1 to 6.6 Name: _______________________________

Check!
Have you have completed the following exercises?
Exercise 6.1
Exercise 6.2
Exercise 6.3
Exercise 6.4
Exercise 6.5
Exercise 6.6

Locate and complete any outstanding exercises then attach your responses to
this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your
responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open Learning
Program (OLP) refer to the Learners Guide to determine which exercises you
need to return to your teacher along with the Mark Record Slip.

Part 6: Telecommunications engineering communications 37

38 Telecommunications engineering
 10/4/03Arial

Bibliography

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AS 1100.201 1992 Technical Drawing Part 201 Mechanical engineering

drawing

AS 1100.301 1992 Technical Drawing Part 301 Architectural drawing

AS 1100.501 1992 Technical Drawing Part 501 Structural engineering

drawing

Avner, S.A. 1974, Introduction to Physical Metallurgy; McGraw-Hill,

Singapore.

Benade, A. H. 1976, Fundamentals of Musical Acoustics, Oxford University

Press, London.

Board of Studies, 1999, Engineering Studies Stage 6 Examination, Assessment

and Reporting, Board of Studies NSW, Sydney.

Board of Studies, 1999, Engineering Studies Stage 6 Specimen Paper, Board

of Studies NSW, Sydney.

Board of Studies, 1999, Engineering Studies Stage 6 Syllabus, Board of

Studies NSW, Sydney.

Brown, B. and Carr P. 1979, Electronics; a practical introduction, Heinemann

Educational Australia, Victoria.

Davis, Troxell & Wiskocil. 1964, The Testing and Inspection of Engineering
Materials , McGraw-Hill, Tokyo.

Duncan, T. 1989, GCSE Electronics, John Murray,

London.

Duncan, T. 1991, Electronics for Today and Tomorrow, John Murray,

London.

Duncan, T. 1993, Electronics for Today and Tomorrow, John Murray,

London.

Encyclopaedia Britannica CD 99. 1999. [CD-ROM].

Halliday, D. and Resnick, R. 1966,Physics, John Wiley and Sons,

Sydney.

39
 Haykin, S. 1988, Digital Communications, John Wiley and Sons,
New York.

Hibbler, R.C. 1989, Engineering Mechanics Statics, Macmillan,

New York.

Higgins, R.A. 1987, Materials for the Engineering Technician, Edward Arnold,
London.

Hioki, W. 2001,Telecommunications, Prentice-Hall Inc,

New Jersey.

Holden, R. 1991, A Guide to Engineering Mechanics, Science Press,

Marrickville, NSW.

Illingworth, V. 1999, The Penguin Dictionary of Electronics, Penguin Books,

United Kingdom.

Jacobowitz, H. 1972, Electronics Made Simple, Doubleday and Co,

London.

Jensen, P.R. 2000, From the Wireless to the Web, UNSW Press,
Sydney.

John, V.B. 1985, Introduction to Engineering Materials, Macmillan Publishers

Ltd, London.

Kaplan, W. and Lewis, D.J. 1971, Calculus and Linear Algebra , John Wiley and
Sons, New York.

Mackie, D. and Hayes P. 1987, Communications, CHP Books,

Burlington.

Mullins R, K. 1983, Engineering Mechanics, Longman,

United Kingdom.

Rochford, J. 2000, Engineering Studies Students Handbook, KJS

Publications, Gosford.

Schlenker, B. and McKern, D. 1983, Introduction to Engineering Mechanics,

Jacaranda Press, Sydney.

Schlenker, B.R. 1974, Introduction to Materials Science, Wiley,

Sydney.

Serritella, M. 1977, Operation Electronics Manual, Macmillan,

South Melbourne.

Stallings, W. 2000, Data and Computer Communications, Prentice-Hall

International, New Jersey.

Stallings, W. 2001,Business Data Communications, Prentice-Hall International,

New Jersey.

Soden, F.A. et al, 1996, 100 Years of the Telephone 18961976, Wellman
Printing Co Pty Ltd, Victoria.

Taylor, A. Barry, O. 1975, Fundamentals of Engineering Mechanics,

Cheshire, Melbourne.

40
10/4/03Arial

Telecom Australia, 1981, Engineer Development Programme, South

Melbourne.

University of Newcastle, 2001, Digital Communications Lecture Notes, Department

of Electrical and Computer Engineering, University of Newcastle NSW.

World Book Encyclopaedia, 1985, World Book, United States of

America.

Wolf, L. 1990, Statistics and Strength of Materials: a parallel approach to

understanding structures, Merrill, New York.

World Book Multimedia Encyclopedia, 1998. [CD-ROM]

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<http://borworld.usbr.gov/power/data/fist/fist3~1/3~1_2.htm>

<http://floti.bell.ac.uk/MathsPhysics/3fibre.htm>

<http://innovations.copper.org/metallurgy/wiremetallurgy.html>

<http://www.datacottage.com/nch/fibre.htm>

<http://www.isoc.org/internet/history>

<http://www.privateline.com>

<http://www.telstra.com.au/classroom.htm>

<http://www.voicendata.com/nov96/4hk0221101.html>

<http://wwwprsc.usm.edu/macrog/electron.html>

41
42
 10/4/03Arial

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44
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