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Digital Communication > ASK, PSK, FSK etc > Flashcards

ASK, PSK, FSK etc Flashcards

1
Q

In DPSK technique, the technique used to encode bits is

a. AMI
b. Differential code
c. Uni polar RZ format
d. Manchester format

A

Differential code

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2
Q

The sequence of operations in which PCM is done is

a. Sampling, quantizing, encoding
b. Quantizing, encoding, sampling
c. Quantizing, sampling, encoding
d. None of the above

A

Sampling, quantizing, encoding

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3
Q

In PCM, the parameter varied in accordance with the amplitude of the modulating signal is

a. Amplitude
b. Frequency
c. Phase
d. None of the above

A

None of the above

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4
Q

One of the disadvantages of PCM is

a. It requires large bandwidth
b. Very high noise
c. Cannot be decoded easily
d. All of the above

A

It requires large bandwidth

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5
Q

The expression for bandwidth BW of a PCM system, where v is the number of bits per sample and fm is the modulating frequency, is given by

a. BW ≥ vfm
b. BW ≤ vfm
c. BW ≥ 2 vfm
d. BW ≥ 1/2 vfm

A

BW ≥ vfm

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6
Q

The error probability of a PCM is

a. Calculated using noise and inter symbol interference
b. Gaussian noise + error component due to inter symbol interference
c. Calculated using power spectral density
d. All of the above

A

All of the above

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7
Q

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

A

Both a and c are correct

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8
Q

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

a. Delta modulation
b. PCM
c. DPCM
d. PAM

A

Delta modulation

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9
Q

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

A

N times the sampling frequency

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10
Q

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

a. Accumulator
b. Sampler
c. PLL
d. Quantizer

A

Accumulator

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11
Q

DPCM is a technique

a. To convert analog signal into digital signal
b. Where difference between successive samples of the analog signals are encoded into n-bit data streams
c. Where digital codes are the quantized values of the predicted value
d. All of the above

A

All of the above

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12
Q

DPCM suffers from

a. Slope over load distortion
b. Quantization noise
c. Both a & b
d. None of the above

A

Both a & b

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13
Q

The noise that affects PCM

a. Transmission noise
b. Quantizing noise
c. Transit noise
d. Both a and b are correct

A

Both a and b are correct

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14
Q

The factors that cause quantizing error in delta modulation are

a. Slope overload distortion
b. Granular noise
c. White noise
d. Both a and b are correct

A

Both a and b are correct

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15
Q

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

A

Adaptive delta modulation

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16
Q

The digital modulation scheme in which the step size is not fixed is

a. Delta modulation
b. Adaptive delta modulation
c. DPCM
d. PCM

A

Adaptive delta modulation

17
Q

In Adaptive Delta Modulation, the slope error reduces and

a. Quantization error decreases
b. Quantization error increases
c. Quantization error remains same
d. None of the above

A

Quantization error increases

18
Q

T1 carrier system is used

a. For PCM voice transmission
b. For delta modulation
c. For frequency modulated signals
d. None of the above

A

For PCM voice transmission

19
Q

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

A

Same as the bandwidth of baseband signal

20
Q

Coherent detection of binary ASK signal requires

a. Phase synchronization
b. Timing synchronization
c. Amplitude synchronization
d. Both a and b

A

Both a and b

21
Q

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

a. Higher
b. Lower
c. Same
d. Not predictable

A

Higher

22
Q

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. 2Π
d. 0

A

Π

23
Q

BPSK system modulates at the rate of

a. 1 bit/ symbol
b. 2 bit/ symbol
c. 4 bit/ symbol
d. None of the above

A

1 bit/ symbol

24
Q

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

A

1 and 0 logic levels

25
Q

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

A

Bipolar NRZ format

26
Q

The bandwidth of BFSK is ______________ than BPSK.

a. Lower
b. Same
c. Higher
d. Not predictable

A

Higher

27
Q

In Binary FSK, mark and space respectively represent

a. 1 and 0
b. 0 and 1
c. 11 and 00
d. 00 and 11

A

1 and 0

28
Q

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

A

50 to 1000 Hz

29
Q

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

A

Two ASK spectra

30
Q

The maximum bandwidth is occupied by

a. ASK
b. BPSK
c. FSK
d. None of the above

A

FSK

31
Q

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 requirement

A

2 bits

32
Q

The data rate of QPSK is ___________ of BPSK.

a. Thrice
b. Four times
c. Twice
d. Same

A

Twice

33
Q

QPSK system uses a phase shift of

a. Π
b. Π/2
c. Π/4
d. 2Π

A

Π/2

34
Q

Minimum shift keying is similar to

a. Continuous phase frequency shift keying
b. Binary phase shift keying
c. Binary frequency shift keying
d. QPSK

A

Continuous phase frequency shift keying

35
Q

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

A

Half of the bit rate

36
Q

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

a. MSK
b. BPSK
c. Gaussian minimum shift keying
d. BFSK

A

Gaussian minimum shift keying

37
Q

Define PWM

A

PWM is basically pulse width modulation. Width of the pulse changes according to amplitude of the modulating signal. It also referred as pulse duration modulation or PDM.

38
Q

Mention the merits of DPCM

A

1.Bandwidth requirement of DPCM is less compared to PCM. 2.Quantization error is reduced because of prediction filter 3.Numbers .of bits used to represent .one sample .value are also reduced compared to PCM

39
Q

What is the difference between PSK and FSK?

A

In PSK, phase of the carrier is switched according to input bit sequence. In FSK frequency of the carrier is switched according to input bit sequence. FSK needs double of the bandwidth of PSK.

Digital Communication (16 decks)

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