# Communication Systems MCQ Questions & Answers

Communication Systems MCQs : This section focuses on the "Communication Systems". These Multiple Choice Questions (MCQs) should be practiced to improve the Communication Systems skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.

Question 1

c(t) and m(t) are used to generate an FM signal. If the peak frequency deviation of the generated FM signal is three times the transmission bandwidth of the AM signal, then the coefficient of the term cos [2p(1008 x 103t)] in the FM signal (in terms of the Bessel Coefficients) is

A. 5 J4(3)
B. J8(3)
C. J8(4)
D. 5 J4(6)

Question 2

The colour subcarrier and sidebands produced by its modulation with the chrominance signals are accommodated in the standard channel width by the process of

B. frequency interleaving
C. frequency changing
D. frequency amalgamation

Question 3

Degaussing in a picture tube means

A. Adding magnetism in mask and mounting frame
B. Removing residual magnetism in mask, shield etc...
C. Increasing resistance of coils to decrease time constant
D. Decreasing resistance of coils to increase time constant.

Question 4

A generator is feeding power to a transmission line of characteristic impedance Z0. The line is terminated in impedance ZL. Standing waves will be set up if

A. ZL = Z0
B. ZL < Z0
C. ZL > Z0
D. both (b) and (c)

Question 5

The rate at which information can be carried through a communication channel depends on

A. carrier frequency
B. bandwidth
C. transmission loss
D. transmitted power

Question 6

For attenuation of high frequencies we should use

A. shunt capacitance
B. series capacitance
C. inductance
D. resistance

Question 7

In colour TV receiver, varactor diode is used for

A. detection
B. rectification
C. tuning
D. both (a) and (b)

Question 8

A carrier is simultaneously modulated by two sine waves having modulation indices of 0.4 and 0.3. The total modulation index will be

A. 0.1
B. 0.7
C. 0.5
D. 0.35

Question 9

When the channel is noisy, producing a conditional probability of error p = 0.5; the channel capacity and entropy function would be, respectively,

A. 1 and 1
B. 1 and 0.5
C. 0.5 and 1
D. 0 and 1

Question 10

In FM signal with a modulation index mf is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of

A. mf
B. 3mf
C. mf/3
D. mf/9

Question 11

Which of the following cannot be the Fourier series expansion of a periodic signal?

A. x(t) = 2 cos t + 3 cos 3t
B. x(t) = 2 cos pt + 7 cos t
C. x(t) = cos t + 0.5
D. x(t) = 2 cos 1.5pt + sin 3.5 pt

Question 12

VSB modulation is preferred in TV because

A. it reduces the bandwidth requirement to half
B. it avoids phase distortion at low frequencies
C. it results in better reception
D. none of the above

Question 13

A carrier wave carries information.

A. TRUE
B. FALSE

Question 14

Consider the following statements The amplitude of an FM wave is constantFM is more immune to noise than AMFM broadcasts operate in upper VHF and UHF frequency rangesFM transmitting and receiving equipments are simpler as compared to AM transmitting and receiving equipments Which of the above are correct?

A. 1, 2, 3, 4
B. 1, 2, 3
C. 2, 3, 4
D. 1, 3, 4

Question 15

Tracking of extra terrestrial objects requires

A. high transmitting power
B. very sensitive receiver
C. fully steerable antenna
D. all of the above

Question 16

A. amplitude modulation
B. frequency modulation
C. both amplitude and frequency modulation
D. neither amplitude nor frequency modulation

Question 17

Energy content of atmospheric noise

A. does not depend on frequency
B. decreases as frequency is increased
C. increases as frequency is increased
D. either (a) or (c) depending on the temperature

Question 18

In radar systems PRF stands for

A. Power Return Factor
B. Pulse Return Factor
C. Pulse Repetition Frequency
D. Pulse Response Factor

Question 19

In sound recording the degree of pre-emphasis is about 6 dB/ octave.

A. TRUE
B. FALSE

Question 20

Which of the following is the indirect way of FM generation?

A. Reactance bipolar transistor modulator
B. Armstrong modulator
C. Varactor diode modulator
D. Reactance FM modulator

Question 21

If the frequency of a wave 20 Hz, the time period is

A. 20 secs
B. 2 secs
C. 0.2 secs
D. 0.05 secs

Question 22

Non-coherently detection is not possible for

A. PSK
C. FSK
D. both (a) and (c)

Question 23

Which of the following has the highest input impedance?

A. CE
B. CB
C. CC
D. Push pull

Question 24

Direct and reflected sound waves may interfere with each other.

A. TRUE
B. FALSE

Question 25

A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is

A. 400 W
B. 512 W
C. 588 W
D. 650 W

Question 26

Which of the following is taken as reference antenna for directive gain?

A. Half wave dipole
B. Elementary doublet
C. Isotropic
D. Infinitesimal dipole

Question 27

Signal to noise ratio of microphone is defined as the ratio of output when the sound pressure is __________ to the output in the absence of any sound signal.

A. 0.5 Pa
B. 0.2 Pa
C. 0.1 Pa
D. 0.01 Pa

Question 28

A cordless telephone using separate frequencies for transmission in base and portable units is known as

A. duplex arrangement
B. half duplex arrangement
C. either (a) or (b)
D. neither (a) nor (b)

Question 29

Frequency shift keying is used mostly in

A. telegraphy
B. telephony
C. satellite communication

Question 30

If the bandwidth is increased by 2, the γFM γAM (where γ is the ratio of SNR of output to SNR at input, FM is frequency modulation and AM is amplitude modulation) is increased by a factor of

A. 2
B. 3
C. 4
D. 6

Question 31

Assertion (A): Free space does not interfere with normal radiation and propagation of radio wavesReason (R): Free space has no magnetic or gravitational fields.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

Question 32

An earth mat for a communication tower consists of

A. one or two radials extending from base of tower at a depth of about 5 cm below ground
B. a large number of radials extending from base of tower at a depth of about 3 m
C. a large number of radials extending from base of tower at a depth of about 30 cm
D. none of the above

Question 33

Some types of traps used in video IF amplifier of colour TV are

A. shunt traps
B. series traps
C. absorption traps
D. all of the above

Question 34

Push pull amplifier is

A. voltage amplifier
B. current amplifier
C. power amplifier
D. none of the above

Question 35

The velocity of sound waves in air

A. is constant at all temperatures
B. varies directly as temperature
C. varies inversely as absolute temperature
D. varies directly as square root of absolute temperature

Question 36

As the frequency increases, the absorption of ground wave by earth's surface

A. decreases
B. increases
C. remains the same
D. either (a) or (c)

Question 37

It is desired that transmission line and load should match for a range of frequencies. The best method is

A. to use a balun
B. to use a single stub of adjustable position
C. to use a double stub
D. to use a broad band amplifier

Question 38

In standing wave pattern on a transmission line

A. voltage and current nodes coincide
B. voltage and current antinodes coincide
C. voltage nodes and current antinodes as well as current nodes and voltage antinodes coincide
D. both (a) and (b)

Question 39

A 1000 kHz carrier is simultaneously modulated with 300 Hz, 800 Hz and 2 kHz audio sine waves. Which of the following frequency is least likely to be present in the output?

A. 1002 kHz
B. 1000 kHz
C. 999.2 kHz
D. 998.0 kHz

Question 40

The number of noise sources in a BJT are

A. 3
B. 2
C. 1
D. 4

Question 41

In CCIR-B system, the time between start of one H syn. pulse and next is

A. 64 μs
B. 6.4 μs
C. 640 μs
D. 0.64 μs

Question 42

Space wave may be a direct wave or wave reflected from earth.

A. TRUE
B. FALSE

Question 43

A modem is classified as low speed if data rate handled is

A. upto 100 bps
B. upto 250 bps
C. upto 400 bps
D. upto 600 bps

Question 44

A woofer should be fed from the input through a

A. low pass filter
B. high pass filter
C. band pass filter
D. band stop filter

Question 45

A telephone exchange has 9000 subscribers. If the number of calls originating at peak time is 10, 000 in one hour, the calling rate is

A. 0.9
B. 10-Sep
C. 0.81
D. 0.1

Question 46

The range of a cordless telephone is about

A. 1000 m
B. 500 m
C. 100 m
D. 10 m

Question 47

Counterpoise is used in coils having

A. high resistivity
B. low resistivity
C. medium resistivity
D. both (b) and (c)