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
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 2
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 3
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 4
A carrier wave carries information.
A. TRUE
B. FALSE
Question 5
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 6
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 7
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 8
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 9
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 10
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 11
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 12
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 13
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 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
Counterpoise is used in coils having
A. high resistivity
B. low resistivity
C. medium resistivity
D. both (b) and (c)
Question 16
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 17
Direct and reflected sound waves may interfere with each other.
A. TRUE
B. FALSE
Question 18
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 19
For attenuation of high frequencies we should use
A. shunt capacitance
B. series capacitance
C. inductance
D. resistance
Question 20
Frequency shift keying is used mostly in
A. telegraphy
B. telephony
C. satellite communication
D. radio transmission
Question 21
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 22
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 23
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
Question 24
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 25
In colour TV receiver, varactor diode is used for
A. detection
B. rectification
C. tuning
D. both (a) and (b)
Question 26
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 27
In radar systems PRF stands for
A. Power Return Factor
B. Pulse Return Factor
C. Pulse Repetition Frequency
D. Pulse Response Factor
Question 28
In sound recording the degree of pre-emphasis is about 6 dB/ octave.
A. TRUE
B. FALSE
Question 29
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 30
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 31
Non-coherently detection is not possible for
A. PSK
B. ASK
C. FSK
D. both (a) and (c)
Question 32
Push pull amplifier is
A. voltage amplifier
B. current amplifier
C. power amplifier
D. none of the above
Question 33
Radio broadcasts are generally
A. amplitude modulation
B. frequency modulation
C. both amplitude and frequency modulation
D. neither amplitude nor frequency modulation
Question 34
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 35
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 36
Space wave may be a direct wave or wave reflected from earth.
A. TRUE
B. FALSE
Question 37
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
Question 38
The number of noise sources in a BJT are
A. 3
B. 2
C. 1
D. 4
Question 39
The range of a cordless telephone is about
A. 1000 m
B. 500 m
C. 100 m
D. 10 m
Question 40
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 41
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 42
Tracking of extra terrestrial objects requires
A. high transmitting power
B. very sensitive receiver
C. fully steerable antenna
D. all of the above
Question 43
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 44
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 45
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 46
Which of the following has the highest input impedance?
A. CE
B. CB
C. CC
D. Push pull
Question 47
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 48
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