Analog Communication System MCQs

Question 1

Which of the following statement about FM is false?

Accepted Answer

A FM signal with a modulation index Mr is passed through a frequency tripper. The modulation index of the output of the tripler will be

Answer

The loudest sound produces maximum frequency deviation

Answer

The audio modulating frequency determines the rate of frequency swing

Answer

None of the above

Question 2

An FM signal with a deviation a is passed through a mixer, and has its frequency reduced six fold. The deviation in the output of the mixer will be

Accepted Answer

a

Answer

6 a

Answer

4a

Answer

indeterminate

Question 3

Pre-emphasis is used to amplify

Accepted Answer

high frequency

Answer

low frequency

Answer

both (a) and (b) above

Answer

none of the above

Question 4

In the stablized reactance modulator AFC system

Accepted Answer

the discriminator frequency must not be too low, or the system will fail

Answer

the discriminator must have a fast time constant to prevent demodulation

Answer

the higher the discriminator frequency, the better the oscillator frequency stability

Answer

phase modulation is converted into FM by the equalizer circuit

Question 5

An FM signal has a frequency deviation of 20 kHz produced by 2 V audio signal of 4000 Hz. What will be the modulation index?

Accepted Answer

5

Answer

2.5

Answer

4

Answer

10

Question 6

De-emphasis circuit is used

Accepted Answer

for de-emphasising high frequency component

Answer

prior to modulation

Answer

after modulation

Answer

for de-emphasising low frequency component

Question 7

Foster Seelay discriminator uses a

Accepted Answer

double tuned circuit with primary and secondary tuned to the same frequency

Answer

single tuned circuit

Answer

couble tuned circuit with primary and secondary tuned to the different frequency

Answer

none of the above

Question 8

The commercial FM radio broadcast band is

Accepted Answer

88 to 180 MHz

Answer

535 to 1600 kHz

Answer

20 to 80 kHz

Answer

300 to 3000 MHz

Question 9

The difference between PM and FM

Accepted Answer

lies in the different definitions of the modulation index

Answer

lies in the poorer audio response of phase modulation

Answer

is too great to make the two systems compatible

Answer

is purely theorctical because practically both are identical