Digital Communication System MCQs

Question 1

Which is the most common modulation system used for telegraphy?

Accepted Answer

Frequency-shift keying

Answer

Two-tone modulation

Answer

Pulse code modulation

Answer

Single tone modulation

Question 2

For a periodic function, the spectral density and the auto correlation functions are

Accepted Answer

Pourier

Answer

one and the same thing

Answer

Laplace transform pair

Answer

none of the above

Question 3

Frequencyshift keying is used mostly in

Accepted Answer

none of the above

Answer

telephony

Answer

telegraphy

Answer

radio transmission

Question 4

Regarding autocorrelation function which of the following statements is incorrect?

Accepted Answer

It is defined only for periodic signals

Answer

It is an average function

Answer

It is a measure of both time variation and statistical dependence

Answer

None of the above

Question 5

The shape-factor of a filter-response

Accepted Answer

determines the adjacent-channel selectivity of the filter

Answer

cannot be applied to crystal filters

Answer

is the same as the peak-to-valley ratio

Answer

is equal to the 60 dB bandwidth of a mechanical filter

Question 6

In adiode, shot noise current is proprotional to, where I = D.C. diode current

Accepted Answer

Ip3r2

Answer

Ip

Answer

Ip2

Question 7

With reference to 'Time division complex' which of the following statements is correct?

Accepted Answer

It interleaves pulses belonging to different transmissions

Answer

It can be usedwith PCM only

Answer

It stacks several channels in adjecent frequency slots

Answer

It combines five groups into a single super group

Question 8

Which one of the following types of noise gains importance at high frequency?

Accepted Answer

Transit?time noise

Answer

Shot noise

Answer

Random noise

Answer

Impulse noise

Question 9

The 'Wise figure of an amplifier is 3 dB. Its noise temperature will be about

Accepted Answer

290 K

Answer

145 K

Answer

580K

Answer

870 K