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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

For attenuation of high frequencies we should use

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

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Question 2

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

A. TRUE
B. FALSE

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Question 3

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

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Question 4

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

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Question 5

Radio broadcasts are generally

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

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Question 6

Frequency shift keying is used mostly in

A. telegraphy
B. telephony
C. satellite communication
D. radio transmission

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Question 7

In radar systems PRF stands for

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

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Question 8

The number of noise sources in a BJT are

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

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Question 9

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

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Question 10

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

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Question 11

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)

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Question 12

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

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Question 13

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

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Question 14

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

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Question 15

Counterpoise is used in coils having

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

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Question 16

A carrier wave carries information.

A. TRUE
B. FALSE

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Question 17

In a fascimile reproduction time to scan one line is 2 ms. If it has 4% blanking, the visible trace time is

A. 1.92 ms
B. 2.08 ms
C. 50 ms
D. 0.08 ms

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Question 18

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

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Question 19

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

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Question 20

Push pull amplifier is

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

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Question 21

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)

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Question 22

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.

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Question 23

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

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Question 24

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

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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

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Question 26

Direct and reflected sound waves may interfere with each other.

A. TRUE
B. FALSE

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Question 27

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)

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Question 28

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

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Question 29

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)

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Question 30

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

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Question 31

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

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Question 32

The range of a cordless telephone is about

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

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Question 33

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

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

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Question 34

Which of the following has the highest input impedance?

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

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Question 35

Tracking of extra terrestrial objects requires

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

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Question 36

In colour TV receiver, varactor diode is used for

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

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Question 37

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

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Question 38

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

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Question 39

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

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

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Question 40

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)

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Question 41

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

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Question 42

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

A. TRUE
B. FALSE

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Question 43

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

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Question 44

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

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Question 45

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

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Question 46

Non-coherently detection is not possible for

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

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Question 47

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

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Question 48

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

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