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180+ Digital Communication Solved MCQs

These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .

51.

The time interval over which the received signal may be sampled without error may be explained by

A. width of eye opening of eye pattern
B. rate of closure of eye of eye pattern
C. height of the eye opening of eye pattern
D. all of the above
Answer» A. width of eye opening of eye pattern
52.

For a noise to be white Gaussian noise, the optimum filter is known as

A. low pass filter
B. base band filter
C. matched filter
D. bessel filter
Answer» C. matched filter
53.

Matched filters are used

A. for maximizing signal to noise ratio
B. for signal detection
C. in radar
D. all of the above
Answer» D. all of the above
54.

The number of bits of data transmitted per second is called

A. data signaling rate
B. modulation rate
C. coding
D. none of the above
Answer» A. data signaling rate
55.

Pulse shaping is done

A. to control inter symbol interference
B. by limiting the bandwidth of transmission
C. after line coding and modulation of signal
D. all of the above
Answer» D. all of the above
56.

The criterion used for pulse shaping to avoid ISI is

A. nyquist criterion
B. quantization
C. sample and hold
D. pll
Answer» A. nyquist criterion
57.

The filter used for pulse shaping is

A. raised – cosine filter
B. sinc shaped filter
C. gaussian filter
D. all of the above
Answer» D. all of the above
58.

Roll – off factor is defined as

A. the bandwidth occupied beyond the nyquist bandwidth of the filter
B. the performance of the filter or device
C. aliasing effect
D. none of the above
Answer» A. the bandwidth occupied beyond the nyquist bandwidth of the filter
59.

Nyquist criterion helps in

A. transmitting the signal without isi
B. reduction in transmission bandwidth
C. increase in transmission bandwidth
D. both a and b
Answer» D. both a and b
60.

The Nyquist theorem is

A. relates the conditions in time domain and frequency domain
B. helps in quantization
C. limits the bandwidth requirement
D. both a and c
Answer» D. both a and c
61.

The difficulty in achieving the Nyquist criterion for system design is

A. there are abrupt transitions obtained at edges of the bands
B. bandwidth criterion is not easily achieved
C. filters are not available
D. none of the above
Answer» A. there are abrupt transitions obtained at edges of the bands
62.

Equalization in digital communication

A. reduces inter symbol interference
B. removes distortion caused due to channel
C. is done using linear filters
D. all of the above
Answer» D. all of the above
63.

Zero forced equalizers are used for

A. reducing isi to zero
B. sampling
C. quantization
D. none of the abov
Answer» A. reducing isi to zero
64.

The transmission bandwidth of the raised cosine spectrum is given by

A. bt = 2w(1 + α)
B. bt = w(1 + α)
C. bt = 2w(1 + 2α)
D. bt = 2w(2 + α)
Answer» A. bt = 2w(1 + α)
65.

The preferred orthogonalization process for its numerical stability is

A. gram- schmidt process
B. house holder transformation
C. optimization
D. all of the above
Answer» B. house holder transformation
66.

For two vectors to be orthonormal, the vectors are also said to be orthogonal. The reverse of the same

A. is true
B. is not true
C. is not predictable
D. none of the above
Answer» B. is not true
67.

Orthonormal set is a set of all vectors that are

A. mutually orthonormal and are of unit length
B. mutually orthonormal and of null length
C. both a & b
D. none of the above
Answer» A. mutually orthonormal and are of unit length
68.

In On-Off keying, the carrier signal is transmitted with signal value ‘1’ and ‘0’ indicates

A. no carrier
B. half the carrier amplitude
C. amplitude of modulating signal
D. none of the above
Answer» A. no carrier
69.

ASK modulated signal has the bandwidth

A. same as the bandwidth of baseband signal
B. half the bandwidth of baseband signal
C. double the bandwidth of baseband signal
D. none of the above
Answer» A. same as the bandwidth of baseband signal
70.

Coherent detection of binary ASK signal requires

A. phase synchronization
B. timing synchronization
C. amplitude synchronization
D. both a and b
Answer» D. both a and b
71.

The probability of error of DPSK is ______________ than that of BPSK.

A. higher
B. lower
C. same
D. not predictable
Answer» A. higher
72.

In Binary Phase Shift Keying system, the binary symbols 1 and 0 are represented by carrier with phase shift of

A. Π/2
B. Π
C.
D. 0
Answer» B. Π
73.

BPSK system modulates at the rate of

A. 1 bit/ symbol
B. 2 bit/ symbol
C. 4 bit/ symbol
D. none of the above
Answer» A. 1 bit/ symbol
74.

The BPSK signal has +V volts and -V volts respectively to represent

A. 1 and 0 logic levels
B. 11 and 00 logic levels
C. 10 and 01 logic levels
D. 00 and 11 logic levels
Answer» A. 1 and 0 logic levels
75.

The binary waveform used to generate BPSK signal is encoded in

A. bipolar nrz format
B. manchester coding
C. differential coding
D. none of the above
Answer» A. bipolar nrz format
76.

The bandwidth of BFSK is ______________ than BPSK.

A. lower
B. same
C. higher
D. not predictable
Answer» C. higher
77.

In Binary FSK, mark and space respectively represent

A. 1 and 0
B. 0 and 1
C. 11 and 00
D. 00 and 11
Answer» A. 1 and 0
78.

The frequency shifts in the BFSK usually lies in the range

A. 50 to 1000 hz
B. 100 to 2000 hz
C. 200 to 500 hz
D. 500 to 10 hz
Answer» A. 50 to 1000 hz
79.

The spectrum of BFSK may be viewed as the sum of

A. two ask spectra
B. two psk spectra
C. two fsk spectra
D. none of the above
Answer» A. two ask spectra
80.

The maximum bandwidth is occupied by

A. ask
B. bpsk
C. fsk
D. none of the above
Answer» C. fsk
81.

QPSK is a modulation scheme where each symbol consists of

A. 4 bits
B. 2 bits
C. 1 bits
D. m number of bits, depending upon the requireme
Answer» B. 2 bits
82.

The data rate of QPSK is ___________ of BPSK.

A. thrice
B. four times
C. twice
D. same
Answer» C. twice
83.

QPSK system uses a phase shift of

A. Π
B. Π/2
C. Π/4
D.
Answer» B. Π/2
84.

Minimum shift keying is similar to

A. continuous phase frequency shift keying
B. binary phase shift keying
C. binary frequency shift keying
D. qpsk
Answer» A. continuous phase frequency shift keying
85.

In MSK, the difference between the higher and lower frequency is

A. same as the bit rate
B. half of the bit rate
C. twice of the bit rate
D. four time the bit rate
Answer» B. half of the bit rate
86.

The technique that may be used to reduce the side band power is

A. msk
B. bpsk
C. gaussian minimum shift keying
D. bfsk
Answer» C. gaussian minimum shift keying
87.

Analog to digital conversion includes

A. sampling
B. quantization
C. sampling & quantization
D. none of above
Answer» C. sampling & quantization
88.

The process of converting the analog sample into discrete form is called

A. modulation
B. multiplexing
C. quantization
D. sampling
Answer» C. quantization
89.

The modulation techniques used to convert analog signal into digital signal are

A. adm
B. pcm
C. dm
D. all of above
Answer» D. all of above
90.

In Delta modulation,

A. one bit per sample is transmitted
B. all the coded bits used for sampling are transmitted
C. the step size is fixed
D. both a and c are correct
Answer» D. both a and c are correct
91.

In digital transmission, the modulation technique that requires minimum bandwidth is

A. delta modulation
B. pcm
C. dpcm
D. pam
Answer» A. delta modulation
92.

In Delta Modulation, the bit rate is

A. n times the sampling frequency
B. n times the modulating frequency
C. n times the nyquist criteria
D. none of the above
Answer» A. n times the sampling frequency
93.

In Differential Pulse Code Modulation techniques, the decoding is performed by

A. accumulator
B. sampler
C. pll
D. quantizer
Answer» A. accumulator
94.

The crest factor of a waveform is given as –

A. 2 x peak value/ rms value
B. rms value / peak value
C. peak value/ rms value
D. peak value/ 2rms value
Answer» C. peak value/ rms value
95.

The digital modulation technique in which the step size is varied according to the variation in the slope of the input is called

A. delta modulation
B. pcm
C. adaptive delta modulation
D. pam
Answer» C. adaptive delta modulation
96.

Impulse sampling is also called as

A. delta sampling
B. ideal sampling
C. natural sampling
D. both a & b
Answer» D. both a & b
97.

Nyquist Rate is given by

A. 2w
B. 2fmin
Answer» A. 2w
98.

The number of voice channels that can be accommodated for transmission in T1 carrier system is

A. 24
B. 32
C. 56
D. 64
Answer» A. 24
99.

For a line code, the transmission bandwidth must be

A. maximum possible
B. as small as possible
C. depends on the signal
D. none of the above
Answer» B. as small as possible
100.

Scrambling of data is

A. removing long strings of 1’s and 0’s
B. exchanging of data
C. transmission of digital data
D. all of the above
Answer» A. removing long strings of 1’s and 0’s

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