Digital Communication System MCQs

Question 1

PAM signals can be demodulaed by using a

Accepted Answer

a differentiator followed by a LPF

Answer

low pass filter (LPF) alone

Answer

a Schmitt trigger followed by a LPF

Answer

a clipper circuit followed by a LPF

Question 2

For 10-bit PCM system, the signal to quantisation noise ratio is 62 dB. If the number of bits is increased by 2, then the signal to quantisation noise will

Accepted Answer

decrease by 12 dB

Answer

increase by 6 dB

Answer

increase by 12 dB

Answer

decrease by 6 dB

Question 3

A communication channel with additive white Gaussian noise, has a bandwidth of 4 kHz and an SNR of 15. Its channel copacity is

Accepted Answer

16 kbps

Answer

1.6 kbps

Answer

32 kbps

Answer

256 kbps

Question 4

In a PCM system, the number of quantization levels are 16 and the maximum signal frequency is 4 kHz, the bit transmission rate is

Accepted Answer

64 K bits/sec

Answer

(b) 16 K bits/sec

Answer

(c) 32 K bits/sec

Question 5

MODEM stands for

Accepted Answer

modulator ar transmitting side and detector at thereceiving side

Answer

which deals with analog signals and shows digital information

Answer

analog at digital at transmitting side and digital to analog at a receiving side

Answer

a device which deals with digital signals only

Question 6

Which of the following requires a transmitted in a 7 unit code. The synchronizing signal?sampling is done at the rate of 10 Hz. The bandwidth should be

Accepted Answer

PAM

Answer

single channel PPM system

Answer

PDM

Answer

all of these

Question 7

The signal to quantisation noise in a PCM system depends upon

Accepted Answer

Sampling rate

Answer

Number of quantisation levels

Answer

Message signal bandwidth

Answer

None of these

Question 8

The bandwidth of a 'N' bit binary coded PCM signal for modulating a signal having bandwidth of 'f' Hz is

Accepted Answer

NfHz

Answer

? Hz

Answer

N2

Answer

N2fHz

Question 9

PCM systems require regenerative over long distances. The repeaters correct squence of the operations which such a repeater performs is timing,

Accepted Answer

timing, thresholding (decision) and equalization

Answer

making equalization and decision

Answer

equalization, timing and decision making

Answer

none of these