COMMUNICATIONS

Refers to the
sending,
receiving and
processing of
information
through
electronic
means

Block Diagram of a Communications

System

Information
Source

Noise

Recipient or
Destination

Transmitte
r

Channel

Receiver

Information
Source

selects
symbols
(letters,
numbers, words, sounds, etc)
from an alphabet (or ensemble)
of possible symbols
Types of
Information

radio,
telephony,
telegraph,
broadcasting,
radar,
radio,
telemetry, and radio aids for
navigation

Transmitte
r

a
collection
of
electronic
components
and
circuits
designed
to
convert
the
information into
a signal
suitable for transmission over
a given Processes Involved
modulation,
multiplexing,
encoding, encryption, and preemphasis (FM)

Channel
the medium by which the
electronic signal is sent from
one place to another

Receive
r

another collection of electronic

components and circuits that
accept
the
transmitted
message from the channel and
convert it back into a form
understandable by humans

Processes Involved

demodulation, demultiplexing,
decoding, decryption, and
de-emphasis (FM)

Noise
any unwanted form of electrical
energy, random and aperiodic
in character which tends to
mutilate the desired signal

Basic
Requirements

1.Accurate
Communication
2.Fast Communication

Types of
Signal

1.ANALOG
telephone, radio broadcast
or TV signals
2. DIGITAL
comprises of pulses at
discrete intervals of time

Transmission
Paths

1.Line Communication
guided media which
include coaxial cable,
twisted pair, optical fibers
and waveguides
2. Radio Communications
unguided media

Basic Concepts

Frequency
number of
times a
particular
phenomenon
occurs at a
given time
expressed in
hertz (1/1 sec)
Hz

Wavelength
distance between two
points of similar cycles of a
periodic wave
Bandwidth
portion of the
electromagnetic spectrum
occupied by a signal

Nomenclature of Frequency Bands

NAME

FREQUENCIES

METRIC SUBDIVISION

APPLICATIONS

Extremely Low
Frequencies (ELF)

30 300 Hz

Power line transmission

Voice Frequencies
(VF)

300 Hz 3 kHz

Audio

Very Low Frequencies

(VLF)

3 30 kHz

Myriametric waves

Government and military

comms., submarine comms.

Low Frequencies (LF)

30 300 kHz

Kilometric waves
(long waves)

Aeronautical and marine

navigation

Medium Frequencies
(MF)

300 kHz 3 MHz

Hectometric waves
(medium waves)

AM radio broadcast

High Frequencies
(HF)

3 30 MHz

Decametric waves
(short waves)

Shortwave radio broadcast,

amateur radio and CB
comms.

Very High
Frequencies (VHF)

30 300 MHz

Metric waves

FM broadcast

Ultra High
Frequencies (UHF)

300 MHz 3 GHz

Decimetric waves

UHF TV, land mobile services

and cellular telephones,
microwave comms.

Super High
Frequencies (SHF)

3 GHz 30 GHz

Centimetric waves

Satellite comms., personal

communication systems

Extremely High
Frequencies (EHF)

30 300 GHz

Millimetric waves

Radar

*microwave frequency band: 1 GHz to 300 GHz

**frequencies beyond EHF are optical frequencies

Significant Historical Events in Electronic

Communications
DATES

EVENTS

1830

American scientist and professor Joseph Henry transmitted

the first practical electrical signal .

1837

Samuel Finley Breeze Morse invented the Telegraph and

patented it in 1844.

1843

Alexander Bain invented the facsimile.

1847

James Clerk Maxwell

Radiation Theory.

1860

Johann Philipp Reis, a German who produces a device called

Telephone that could transmit a musical tone over a wire to a
distant point but incapable of reproducing it.

1864

James Clerk Maxwell, a Scottish physicist established the

Theory of Radio or Electromagnetism which held the rapidly
oscillating electromagnetic waves exist and travel at through
space with the speed of light.

postulated

the

Electromagnetic

DATES

EVENTS

1875

Thomas Alba Edison invented Quadruplex telegraph, doubling

existing line qualities.
J. M. Emile Baudot invented the first practical Multiplex
Telegraph and another type of telegraphy codes which
consisted of pre arranged 5 - unit dot pulse.
A. C. Cowper introduced the first Facsimile Machine or writing
telegraph using a stylus.

1876

Alexander Graham Bell and Thomas A. Watson invented the

Telephone capable of transmitting voice signals (March 10).

1877

Thomas Edison invented the Phonograph.

1878

Francis Blake invented the Microphone Transmitter using

platinum point bearing against a hard carbon surface.

1882

Nikola Tesla outlined the basic principles of radio transmission

and reception.

1887

Heinrich Hertz detected electromagnetic waves with an

oscillating circuit and establishes the existence of radio
waves.

DATES

EVENTS

1889

Hertz discovered the progressive propagation of

electromagnetic action through space using a spark gap
wave generator, to measure the length and velocity of
electromagnetic waves and their direct relation to light and
heat as their vibration, reflection, refraction and polarization.

18790

Almon Strowger introduced the dial switching system

transmitting the desired telephone number electrically
without the assistance of a human telephone operator.

1895

Marchese Guglielmo Marconi discovered ground wave radio

signals.

1898

Guglielmo Marconi established the first radio link between

England and France.

1901

Reginald A. Fessenden transmits the worlds first radio

broadcast using continuous waves. Marconi transmits
telegraphic radio messages from Cornwall, England to
Newfoundland, first successful transatlantic transmission of
radio signals.

1904

John Ambrose Fleming invented the Vacuum Tube Diode.

DATES

EVENTS

1906

Reginald Fessenden invented Amplitude Modulation (AM).

Lee De Forest added a grid to the diode and produced triode.
Ernst F. W. Alexanderson invented the Tuned Radio Frequency
Receiver (TRF) an HF Alternator to producing AC contributing
to better voice broadcasting.

1907

Reginald Fessenden developed the Heterodyne Receiver.

1918

Edwin H. Armstrong invented the Superheterodyne Receiver.

1923

J. L. Baird and C. F. Jenkins demonstrated the transmission of

Black and White Silhouettes in motion. Vladymir Zworykin
and Philo Farnsworth developed television cameras, the
Iconoscope and the Image Detector. The first practical
television was invented in 1928.

1931

Edwin Armstrong invented the Frequency Modulation, greatly

improving the quality of the signals.

1937

Alec Reeves invented the Pulse Code Modulation for digital

encoding of PCM signals.

1945

Arthur C. Clarke proposed the use of satellites for long

distance radio transmissions.

DATES

EVENTS

1946

AT&T introduced the first mobile telephone system for the

public called the MTS (Mobile Telephone System).

1947

John Bardeen, Walter Brattain and William Shockley

introduced the bipolar junction transistors which started a
new trend in radio receiver design; December 4.

1951

First transcontinental microwave system began operation.

1954

J. R. Pierce showed how satellites could orbit around the earth

and effect transmission with earth stations.

1957

Troposcatter Radio Link was established between Florida and

Cuba by using antennas and high powered transmitters to
force microwaves beyond LOS obstructed by earths
curvature bulge.
Russia launched Sputnik I, the first active earth satellite,
capable of receiving, amplifying and retransmitting
information to earth stations.

1958

Jack Kilby developed the first Monolithic Integrated Circuit

Semiconductor chip with active and passive elements.

1959

Robert Noyce invented the Very Large Scale Integrated Circuit

(VLSIC).

DATES

EVENTS

1962

AT&T launched Telstar I, the first satellite to received and

transmit simultaneously. A year later, Telstar II was launched
and used for telephone, TV fax and data transmission .

1965

COMSAT and INTELSAT launched the first communications

satellite code name Early Bird at approximately 34000 km
above sea level.

1967

K. C. Kao and G. A. Bockam of Standard Telecommunications

Laboratories in England proposed the use of cladded fiber
cables as new transmission medium.

1977

First commercial use of optical fiber cables

1983

Cellular telephone networks introduced.

1991

Tim Berners Lee developed World Wide Web (WWW).

Self Test

Principles of
Communications
Choose the letter which answer each
question.

1. He is recognized as the Father of Electromagnetism

a. Joseph Henry
b. Andre Marie Ampere
c. Hans Christian Oersted
d. Michael Faraday
2. An American scientist who discovered electromagnetic
self induction. He was a pioneer of modern forecasting
techniques.
a. Joseph Henry
b. Andre Marie Ampere
c. Hans Christian Oersted
d. Michael Faraday

Self Test

Principles of
Communications
Choose the letter which answer each
question.

3. He discovered Photoelectricity through a photosensitive

element, Selenium that could carry current in direct
proportion to the amount of light that struck it.
a. Jonas Jacob Berzelius
b. Charles Babbage
c. James Maxwell
d. Michael Faraday
4.

The Father of Electrodynamics who exposed the

phenomenon of electromagnetism following the discovery
of magnet needle by Oersted.
a. Joseph Henry
b. Andre Marie Ampere
c. James Maxwell
d. Michael Faraday

Self Test

Principles of
Communications
Choose the letter which answer each
question.

5. The range of frequencies represented in a signal to

convey information.
a. Beam width
b. Crisp
c. Guard band
d. Bandwidth
6. It refers to the sending, receiving and processing of
information by electronic means
a. Communications
b. Telemetry
c. Telephony
d. Broadcasting

Self Test

Principles of
Communications
Choose the letter which answer each
question.

7. The big breakthrough in electronics communications came

with the invention of the ____________ in 1844.
a. Transistor
b. Phonograph
c. Telegraph
d. Telephone
8. Term for transmission of printed picture by radio
a. Facsimile
b. ACSSB
c. Xerography
d. Television

Self Test

Principles of
Communications
Choose the letter which answer each
question.

9. A Scottish physicist who established the Theory of Radio

or Electromagnetism which held that rapidly oscillating
electromagnetic waves exist and travel at through space
with the speed of light.
a. James Maxwell
b. Andre Marie Ampere
c. Hans Christian Oersted
d. Michael Faraday
10. The first words transmitted over the telephone
a. Mr. Watson, come here, I want you
b. What God has wrought
c. This is the day
d. None of these

Self Test

Principles of
Communications
Choose the letter which answer each
question.

11. Most of the communications receiver is in form of

____________ type.
a. Superheterodyne
b. TRF
c. Single ended
d. High level
12. He was the one who developed the wireless telegraph.
a. Edison
b. Armstrong
c. Marconi
d. Bell

Self Test

Principles of
Communications
Choose the letter which answer each
question.
13. He invented the first practical Multiplex Telegraph

and
another type of telegraphy codes which consisted of pre
arranged 5 unit dot pulse patterns. This multiplexer
allowed signals of up to 6 different telegraph machines to
be transmitted over a single wire pair.
a. JM Emile Baudot
b. AC Cowper
c. Thomas Edison
d. Thomas Doolittle

14. Introduced the first Facsimile

telegraph using stylus.
a. JM Emile Baudot
b. AC Cowper
c. Thomas Edison
d. Alexander Graham Bell

Machine

or

writing

Self Test

Principles of
Communications
Choose the letter which answer each
question.

15. Invented the Microphone transmitter using platinum

point bearing against a hard carbon surface
a. Francis Blake
b. Thomas Watson
c. Thomas Doolittle
d. Henry Hunnings
16. What type of field does Faraday shield stop?
a. Common
b. Array
c. Electrostatic
d. Magnetostatic

Self Test

Principles of
Communications
Choose the letter which answer each
question.

17. Which of the following is not normally tested in a

transmitter?
a. Power
b. Modulation
c. Frequency
d. Amplitude
18. What other term
beating?
a. Heterodyning
b. Scrambling
c. Filtering
d. Suppressing

is

essentially

synonymous

with

Self Test

Principles of
Communications
Choose the letter which answer each
question.

19. Term in Communication that is referred to send in all

directions.
a. Announce
b. Broadcast
c. Transmit
d. Media
20. Invented the telephone transmitter using granular
carbon and thin platinum diaphragm and a gold plated
electrode
a. Nikola Tesla
b. Henry Hunnings
c. Thomas Watson
d. AC Cowper

Self Test

Principles of
Communications
Choose the letter which answer each
question.
21.
He introduced the Dial Switching System, transmitting

the desired telephone number electrically without the

assistance of a human telephone operator
a. Thomas Edison
b. Almon Strowger
c. JJ Thomson
d. Lee De Forest

22. An Italian physicist who invented the first wireless

telegraph, initially transmitting messages over a distance
of 1 mile but later improved it to 8000 miles in 1902. He
also made the first successful transatlantic radio
transmission.
a. Francis Blake
b. Ernst Alexanderson
c. KF Braun

Self Test

Principles of
Communications
Choose the letter which answer each
question.

23. The Father of Quantum Theory. He introduced the

revolutionary idea that the energy emitted by an
oscillator could take only on discrete values or quanta
a. Guglielmo Marconi
b. John Fleming
c. Max Karl Ernst Ludwig Planck
d. Christian Hulsmeyer
24. Who developed the CRT capable of tracing curves on
phosphor screen?
a. John Fleming
b. Max Karl Ernst Ludwig Planck
c. KF Braun
d. Christian Hulsmeyer

Self Test

Principles of
Communications
Choose the letter which answer each
question.
25. He invented the superheterodyne receiver
a. Edwin Armstrong
b. Alec Reeves
c. Veldemar Poulsen
d. Boris Rosing

26. He developed a simple radio echo device to prevent ship

collisions. He was considered as the forerunner of RADAR
a. Veldemar Poulsen
b. Christian Hulsmeyer
c. Boris Rosing
d. Reginald Fessenden

Self Test

Principles of
Communications
Choose the letter which answer each
question.

27. Who invented the Pulse Code Modulator for digital

encoding of PCM signals
a. Alec Reeves
b. Edwin Armstrong
c. Boris Rosing
d. Reginald Fessenden
28. He was the one who developed the mathematical
solution to a complex repetitive waveform
a. Carson
b. P. H. Smith
c. J. Fourier
d. Y. Uda

Self Test

Principles of
Communications
Choose the letter which answer each
question.

29. The volume of transaction proceed in a specific unit of

time
a. Response time
b. Throughout
c. Availability
d. Reliability
30. ____________ is a device that measures the internal open
circuit voltage of an equivalent noise generator having an
impedance of 600 ohms and delivering noise power to a
600 ohms load.
a. Phosphometer
b. Barometer
c. Reflectometer
d. Voltmeter

MODULATION
mixing
of
low
frequency
signals
modulating
signal)
with high frequency
signals
(carrier
signal)

process by which
some characteristic of
a high frequency sine
wave is varied in
accordance with the
instantaneous
value
of the signal

imposition of
information on a
given signal

modification of one
signal by another
signal

Types of
Modulation

a. According to carrier
used
1.Pulse
1.Continuous Wave
carrier is a train
carrier is a
of pulses
sinusoid
(discrete)

Types of
Modulation

a. According to the method

used

1.Analog
modulated
parameter is made
proportional to
the
modulating signal

2. Digital
change the form of
a given signal

Reasons for
Modulation
1. To reduce the antenna
lengths
2. To reduce noise / interference
3. For frequency assignments
4. For multiplexing
5. To overcome equipment
limitations

Analog
Modulation
1. Amplitude
Modulation

2. Angle
Modulation
a. Frequency
Modulation

b. Phase
Modulation

Digital
Modulation
1. Pulse Code
Modulation

2. Delta
Modulation

Consider any
sinusoid
(t)= V sin (t
+ )
= instantaneous
amplitude
V = peak amplitude
= 2f; angular
frequency
t = instantaneous time
= phase angle in
radians

amplitude
phase
t = 1/f

NOTE
Any type of modulation should be
reversible
(get back to the original signal) by

Basic Emission Classification

First Symbol Type of Modulation of the Main
Carrier
Emission of unmodulated carrier
N
Emission in which the main carrier is amplitude
-> Double sideband

-> Single sideband, full carrier

-> Single sideband, reduced or variable level carrier

-> Single sideband, suppressed carrier

-> Independent sideband

-> Vestigial sideband

Emission in which the main carrier is angled modulated

-> Frequency Modulation

-> Phase Modulation

First Symbol Type of Modulation of the Main

Carrier
Emission in which the main carrier
is angled and amplitude
D
modulated simultaneously
Emission of pulses
-> Sequence of unmodulated pulses

-> Sequence of pulses

->> Modulated in amplitude

->> Modulated in width/duration

->> Modulated in position/phase

->> The carrier is angle modulated during the

period of the pulse

->> Combination of the foregoing or is produced

by other means

Cases not covered above or combination of two or more of

the
following modes: amplitude, angle, angle and phase

Cases otherwise not covered

Second Symbol Nature of the Signals Modulating

the
Main Carrier
No modulating signal
0
Digitally keyed carrier

Digitally keyed tone

Analog

Multichannel digital

Multichannel analog

Combination

Cases not otherwise covered

Third Symbol Type of Information to be

No information transmittedTransmitted

Telegraphy for aural reception

Telegraphy for automatic reception

Facsimile

Data transmission, telemetry, telecommand

Telephony (including sound broadcasting)

Television (video )

Combination of the above

Cases otherwise not covered

Fourth Symbol Details of Signals

Two condition code with elements of differing numbers
and/or durations

Two condition code with elements of the same number

and
duration without error correction

Two condition code with elements of the same number

and
duration with error correction

Four condition code in which each condition represents a

signal element

Multicondition code in which each condition represents a

signal element

Multicondition code in which each condition or combination

of conditions represents a character

Fourth Symbol Details of Signals

Sound of broadcasting quality (monophonic)

Sound of broadcasting quality (stereophonic or

quadraphonic)

Sound of commercial quality

Sound of commercial quality with the use of frequency

inversion or band splitting

Sound of commercial quality with separate frequency

modulated signals to control the levels of
demodulated signal

Monochrome

Color

Combination of the above

Cases not otherwise covered

Fifth Symbol Nature of Multiplexing

None

Code division multiplex

Frequency division multiplex

Time division multiplex

Combination of frequency division multiplex

and
time division multiplex

Other types of multiplexing

AMPLITUDE
MODULATION

A
system
of
modulation
in
which
the
amplitude of the
carrier is made
proportional
to
the
instantaneous
amplitude of the
modulating
voltage.
Carrier voltage is
made
proportional
to
the
instantaneous
modulating
signal

Informatio
n
or
modulatin
g
signal (m)

AM
modulato
r
Carrie
r
(c )

Output
(AM)

General Equation of the AM

wave

let the carrier voltage be given by

c(t) = Vc sin c t
and the modulating voltage be given by

m(t) = Vm sin m
then the amplitude resulting
t from modulation is
A = Vc + m (t) = Vc + Vm
sin m t
Since
Therefore

and Vm = Vc ma, then

A = Vc + Vc ma sin m t
A = Vc (1 + ma sin m t )

The voltage of the resulting AM wave envelope at any instant

is
(t) = A sin
AM

c t

General Form

AM(t) = Vc (1 + ma sin m t)
sin c t
Standard Form
AM(t) = Vc sin c t +
cos (c + m) t

carrier

cos (c - m) t +

lower
sideband
LSB

upper
sideband
USB

where
Vc = carrier signal peak voltage
c = 2 fc = carrier signal angular frequency
m = 2 fm = modulating signal angular frequency
t = instantaneous time
ma = modulation index

Frequency Domain of Standard

AM

graph of relative
amplitude of signal
against frequency
AM(t
)

carrier

LS
B
fc fm

USB
fc

fc + fm

Time Domain of Standard

AM

Envelop
e
the curve produced by joining the tips
of the individual RF cycles of the AM
waveform
envelope

AM Modulation Index
(ma)
Modulation index (modulation factor,
modulation coefficient, degree of
modulation, depth of modulation)

wher
e
; 0 < ma <
1

Percent Modulation
(Ma)
modulation index
expressed as a
percentage
Ma = ma x
100%

Degrees of
Modulation
1. Ma < 100%
undermodulati
on
2. Ma = 100%
modulation

3. Ma > 100%
overmodulation

Example
A modulated wave has a peak value of 2 volts. The
carrier wave equation for the voltage is 1.2 sin(20t + 15).
Determine
whether the signal is overmodulated or not.

Given
Vm = 2 V
Vc = 1.2 V
Solution

ma = 1.67
(overmodulated)

Power Content of an AM
Signal
PT = PC + PUSB +
PLSB
PT = P C

NOTE
PUSB = PLSB
where PUSB = PLSB =
PSBT =

NOTE
PC is constant value before and after
modulation. PT is
the total power after
modulation and is dependent on
the modulation
index. The higher the modulation
index, the

Example
A transmitter supplies 8 kW to the antenna when
unmodulated. Determine the total power radiated when
modulated to 30%.
Given
Pc = 8 kW
ma = 0.3
Solution

PT = 8.36
kW

Current and Voltage

Relationships

where
IC = unmodulated carrier
IT = total or modulated current
VC = unmodulated carrier voltage
VT = total or modulated voltage
ma = modulation index

Example
The antenna current of an AM transmitter is 8 A when
only the carrier is sent, but it increases to 8.93 A when
the carrier
is sinusoidally modulated. Find the
percentage
modulation.

Given
IC = 8 A
IT = 8.93 A

Solution

ma = 0.701

Ma =
70.1%

Simultaneous
Modulation
modulation by several
carrier

where
VT = total modulated voltage
IT = total modulated current
maT = effective total modulation
index

Example
A 360 W carrier is simultaneously modulated by 2
audio waves with modulation percentage of 55 and 65,
respectively. What is the total sideband power radiated?

Given
PC = 360 W
Ma1 = 55%
Ma2 = 65%

Solution

PSBT = 130.5
W

Bandwidth Formula for

AM

BW = 2 x (single carrier modulation)

fm
BW = 2 x
(simultaneous modulation)
fmhighest

Efficienc
y

Percentage Power
Saving

NOTE
Efficiency and power saving depends on the type
of transmission but the total transmitted power is
computed on
the basis of double sideband full

Example
How many AM broadcast stations can be
accommodated in a 100 kHz bandwidth if the highest
modulating frequency is
5 kHz?

Given
BW = 100 kHz
fmhighest = 5 kHz
Solution
BW = 2 x fmhighest
BW = 2 x 5 kHz
BW = 1010
kHz
stations

BOARD
PROBLEMS

A portion in a communications system, which

processes the information so that it will become
suitable to the characteristic of the transmission
medium
a. Encoder
b. Modulation
c. Transmitter
d. Multiplexer

Signal whose physical quantity varies

continuously with time
a. Digital
b. Analog
c. Discrete
d. Information

Is the reduction of signal amplitude as it passed

over the transmission medium?
a. Noise
b. Distortion
c. Attenuation
d. Interface

Signal contamination by extraneous or external

sources, such as, other transmitters, power lines
and machinery.
a. Noise
b. Distortion
c. Harmonics
d. Interference

Noise figure for an amplifier with noise is always

a. 0 dB
b. Infinite
c. Less than 1
d. Greater than 1

Extra-terrestrial noise is observable at

frequencies from
a. 0 to 20 KHz
b. 8 Mhz to 1.43 GHz
c. 5 to 8 GHz
d. 15 to 60 MHz

The outline of the peaks of a carrier has the

shape of the modulating signal and is called the
a. Trace
b. Waveshape
c. Envelope
d. Carrier variation

The values of Vmax and Vmin as read from an AM wave on an

oscilloscope are 2.8 and 0.3. The percentage of the
modulation is
a. 10.7 percent
b. 41.4 percent
c. 80.6 percent
d. 93.3 percent

A carrier of 880 kHz is modulated by a 3.5-kHz

sine wave. The LSB and USB are respectively,
a. 873 and 887kHz
b. 876.5 and 883.5 kHz
c. 883.5 and 876.5 kHz
d. 887 and 873 kHz

An AM signal has a carrier power of 5W. The

percentage of modulation is 80 percent. The total
sideband power is
a. 0.8 W
b. 1.6 W
c. 2.5 W
d. 4.0 W

An AM signal with a maximum modulating signal

frequency of 4.5 kHz as a total bandwidth of
a. 4.5 kHz
b. 6.75 kHz
c. 9 kHz
d. 18 kHz

What is the third character in the emission

designation for telephony?
a. F
b. B
c. D
d. E

An amplifier operating over the frequency range

of 455 to 460 kHz has a 200 k input resistor.
What is the RMS noise voltage at the input to this
amplifier if the ambient temperature is 17C?
a. 40 V
b. 4.0 V
c. 400 V
d. 4.0 mV

What is the noise voltage across a 300 input

resistance to a TV set with a 6 MHz bandwidth
and temperature of 30C?
a. 2.3 V
b. 3.8 V
c. 5.5 V
d. 6.4 V

If bandwidth is doubled, the signal power is _____

a. Doubled
b. Tripled
c. Halved
d. Not changed

If an amplifier has equal input and output

impedances, what voltage ratio does the gain of
50 dB represent?
a. 316.2
b. 325.2
c. 320.1
d. 315.0

A superheterodyne is tuned to 2738 kHz. The IF is

475 kHz. What is the image frequency?
a. 3.09 MHz
b. 4.5 kHz
c. 4385 kHz
d. 3688 kHz

46.What is the standard intermediate frequency

for FM radio?
a) 112 kHz
b) 455 kHz
c) 4.5 kHz
d) 10.7 kHz

Determine from the following radio frequency

that falls under the Very High Frequency band of
the radio spectrum.
a) 450.00 MHz
b) 235.5 MHz
c) 144.50 GHz
d) 345.00 MHz

When an operator wishes to indicate that he has

received all of the last transmission, he will
transmit the word _____.
a) Out
b) Over
c) Ok
d) Roger

If a transmitter supplies 8 kW to the antenna

when it is unmodulated, determine the total
radiated power when modulated at 30%.
a) 5.30 kW
b) 15.65 kW
c) 8.36 kW
d) 20 .15 kW

What is the power saving in J3E system at 100%

modulation?
a) 66.67%
b) 33.3%
c) 100%
d) 83.3%

Determine the power saving in percent when the

carrier is suppressed in an AM signal modulated
to 80%
a) 75.8%
b) 100%
c) 66.7%
d) 80%

The antenna current of an AM transmitter is 6.2 A

when unmodulated and rises to 6.7 A when
modulated. What is the %m?
a) 42.8%
b) 67%
c) 57.9%
d) 51%

Types of AM Transmission
1. A3E Standard AM (DSBFC)
- Double Sideband Full Carrier
- used for broadcasting

2. A3J DSBSC
- Double Sideband Suppressed Carrier

3. H3E SSBFC
- Single Sideband Full Carrier
- could be used as a compatible AM
broadcasting system with A3E receivers
4. J3E SSBSC
- Single Sideband Suppressed Carrier
- The carrier is suppressed by at least 45 dB
in the transmitter

Frequency Domain

Types of AM Transmission
5. R3E SSBRC
- Single Sideband Reduced Carrier
- An attenuated carrier is reinserted into
the
SSB signal to facilitate receiving tuning
and
demodulation.
6. B8E Independent Sideband Emission
- Two independent sidebands, with a carrier
that is most commonly attenuated or
suppressed.
- Used for HF point to point
radiotelephony
in which more than one channel is
required.
7. C3F Vestigial Sideband
- A system in which a vestige, i.e., a trace,
of the
unwanted sideband is transmitted usually
with
a full carrier.
- Used for video transmissions in all the
worlds

Frequency Domain