CHAPTER 1:PRINCIPLES

OFCOMMUNICATIONS

COMMUNICATIONSSYSTEM

It is the sending, processing and receiving information by

electrical or electronic means.
It refers to the basic process of exchanging informationby -
electronic means.

BRIEF HISTORY OF ELECTRONIC COMMUNICATIONS

1799 Alessandro Volta invented the electric battery.

1830 Joseph Henry transmitted the first practical electrical signal over one
mile of wire to activate an electromagnet.
1837 Samuel Finley Breese Morse invented the telegraph.
1843 Alexander Bain invented the facsimile.
1858 Transatlantic cablewas laid and failed.
1875 Emile Baudot designed a fixed-length binary codefor telegraph.
1876 Alexander Graham Bell patented the telephone.
1877 Thomas Alva Edison invented the phonograph.
1864 James Clerk Maxwell predicted mathematically radio propagation.
1880 AlexanderGraham Bell patented the photophone.
1887 Heinrich Hertz verified experimentally Maxwell's theory.
1888 Friedrich Reinitzer invented liquid crystal.
1895 Guglielmo Marconi demonstrated wireless transmission.
1906 Reginald Fessenden invents AM (amplitude modulation).
1920 Radio Station KDKA broadcasts the first regular licensed AM radio
transmission.
1927 Philo Farnsworth produced the first all-electronictelevision
transmission.
1930 Heinrich Lamm was the first to transmit images through a single
glass fiber.
1933 Major Edwin Armstrong invented FM (frequency modulation) radio.
1937 Alec Reeves invented binary coded pulse-code modulation.
1939 First use oftwo-way radio (walkie -talkies).

1940 Invention and perfection ofradar (WorldWar l).

1946 The AT&T (American Telephone and Telegraph Company)

inaugurated the first mobile telephone system for the public known
as Mobile Telephone System.

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 of cellular
the concept telephonybut
1947 AT&T developed the
not yet exist.
the concept did
torealize Hopkins and Narinder
techty
Harold
Abraham van
Heel,
1954 thefiber optics Kapany
which propelled
imogingbundles, revolution
annoy

.
of flexible fiberscope.
to the development
1957 the world's first artificial sotellite,
Russia launched Sputnik
radio first used.
1961 Citizens band
artificial satellite Telstar
1962 NASA lounches its first
television) wasintroducedin
1970 HDTV (high-definition Japan.
Cerfinvented
TCP (transmission
1972 Bob Kahn and Vint control
to wire local proto
1973 Robert Metcalfe invents Ethernet computers
Motorola invented the first togethe
and Martin Cooper
of
practical
mobile
phone.
fiber cables.
1977 Firstcommercialuse ofoptiçal
1982 Internet development
and first use.

1983 opened the first commercial cellular telephone

AT&T systemin the
United States.

1991 Tim Burners-Lee invents the Www(World Wide Web)

1993 First browserMosaic.
1995 Global Positioning System deployed.
1996 First smartphonesby BlackBerry, Nokia, and Palm.
1997 First WLANS (wireless local area networks).
1999 DTV (digital television) transmission begins in the United State:

2009 First fourth-generation LTE (long term evolution) cellular netwo'a

and first 100 Gbps fiber optical networks.

BASIC COMMUNICATIONS SYSTEM

TRANSMISSION
TRANSMITTER RECEVER
NFORMATION CHANNEL RECOVERED

INFORMATION

NOISE

TRANSMITTER

It is a source of information, which must be delivered

or

transmitted to a particular
destination over a channel. that

is a collection
It
one or more electronic devices orcircuits
of
suitable
converts the original source more
information to a form
for transmission
over a particular
transmission medium.
It performs
encoding and modulation.
ESTEntae
Basic Transmitter Components

Modulator - it modulates the signal.

Amplifier- it provides power to the signal.

Oscillator - it providesthe carrier signal.

RECEIVER

It is the destination upon which informationfrom the transmitter

is delivered.

It is acollection of electronic devicesand circuits that accepts the

transmitted signals from the transmissionmedium and then
convertsthose signals back to their original form.
It performs decodingand demodulation.

Basic Receiver Components

Demodulator (Detector) -it demodulates the signal.

Amplifiers - it provides power to the signal.

Output Devices -devices such as speaker,monitor,

printer, etc.

TRANSMISSION CHANNEL (MEDIUM)

It is the path or medium that the information travels from the

transmitter to the receiver means of
(i.e., it provides a

transporting signals between a transmitter and a receiver).

Attenuation (sometimes referred to as power loss) occurs at this
point.

ORIGINAL SIGNAL ATTENUATED SIGNAL AMPLIAIED SIGNAL

AA AA AM
TRANSMISSION MEDIUM

PERCDcLearnhub 5
 Media
ofTransmission
some form of

Classifications with conductor

Media
- those
electromagnetic
Guided in which energyare
conduit
providesa
contained.
Transmission

open-wire
lines,
lines
coaxial
|
(twisted pairs, twin lead,
cables,etc.)

fibercables
Optical

Waveguides

are emitted then radiated

Media -signals
Unguided signals propagating
vocUum(those are available to down
a
air or
through media anyon
transmission them).
the unguided
capableof
receiving

who has a device

Free space
Earth's atmosphere

AMPLIFIER

the signal

capableof increasing
circuit which
is
signal
It is an electronic altering the
appreciably
magnitude oramplitude without
waveform characteristics.

CLASSES OF AMPUFIERS

B CLASS AB CLASSC
CLASS A CLASS

active o little belowcut

cut-off
(linear)
above cut off region
QPoint
region
region off region
between more than
Maximum 25% or 50% 78.5%
&B 90%
class A
Eficiency
between less than
Conduction 360 180
180-359 180
Angle
Distortion low high moderate veryhigh

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STte
OSCILLATOR

Itis acircuit that produces a periodic waveform on its output with

. only the DC supply voltage as an input.

Itis a non-rotating device,for producing alternating current, the

output frequency of which is determined by the characteristics of
the device.
It can be thought of asan amplifier that provides itself (through
feedback) with an inputsignal.

SCILLATOREn

TYPES OF OSCILLATORS

LCOscillators -they used LC network (parallel resonant circuit or

tank circuit) as frequency determiningelement. These are
commonly used at high frequencies.

HartleyOscillator-it usesa tapped coil as its feedback

element.

Colpitts Oscillator - it uses a split capacitoras its

feedback element.

Clapp Oscillator - it is similar with Colpitts with an

additionalcapacitor in series with the inductorin the
feedback circuit.

Armstrong Oscillator it uses a - tickler coil (transformer)

as its feedback element.

RC Oscillators -they used RC networks to provide regenerative

feedback and to determine the frequency of operation.These are
widely used for low frequencies.

Wien Bridge Oscillator - it is a sinusoidal feedback

oscillator that utilizes a lead-lag circuit.

Phase Shift Oscillator -it uses a series of RC sections.

PERCDcLearnhub
Crystal scillators- they used specially-cut
crystals to
usually used toproduce an
frequency.These are contrdi
output b
highly stable and at a very precise frequency. which

FILTER

It is circuit
frequency-selective which are
a designed
topass
frequenciesand reject others. sor

Simplefilters constructed by using resistors and

capacitors or
inductors and capacitors are called passive filters,
because
use passive components that do not amplify. they

Some special types of filters are active filters that use RC

networks with feedback in op-amp circuits, switched

capacitor
filters, crystal and ceramicfilters, surfaceacoustic w
wave(SAW)
filters, and digital filters implemented with digital signal

processing (DSP)techniques.

Basic Types of Filter Circuits

Low-pass Filter - it passesfrequenciesbelow a critiral

frequency called the cutofffrequency and greatly

attenuatesthose above the cutoff frequency.

-
High-pass Filter it passesfrequenciesabove the cutof

but rejects those below it.

Bandpass Filter - it passes frequenciesover a narrow

range between lower and upper cutoff frequencies.

Band-rejectFilter - it rejects or stops frequencies overa

narrow range but allowsfrequenciesabove and below

to
pass.

All-pass Filter - it passes all frequenciesequally well over

its design range but has a fixed or predictable phase shit

characteristic.

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 PERCDeLearnhuERCnc
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8

9
pioneer
electromagnetics.
the

of
in
expressed
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Hert,
a
who
fieldHertz

named
(Hz),

after
frequency
was
measured
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better (cps),
in
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per
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