Electronics and Communication Engineering - Communication Systems

16. 

In radar systems PRF stands for

A. Power Return Factor
B. Pulse Return Factor
C. Pulse Repetition Frequency
D. Pulse Response Factor

Answer: Option C

Explanation:

PRF in radar systems means pulse repetition frequency.


17. 

Which of the following cannot be the Fourier series expansion of a periodic signal?

A. x(t) = 2 cos t + 3 cos 3t
B. x(t) = 2 cos pt + 7 cos t
C. x(t) = cos t + 0.5
D. x(t) = 2 cos 1.5pt + sin 3.5 pt

Answer: Option C

Explanation:

x(t) = cos t + 0.5

not satisfies the Dirichlet condition.

The integration of constant term is ∞.


18. 

Which of the following is the indirect way of FM generation?

A. Reactance bipolar transistor modulator
B. Armstrong modulator
C. Varactor diode modulator
D. Reactance FM modulator

Answer: Option B

Explanation:

It generates FM through phase modulation.


19. 

A telephone exchange has 9000 subscribers. If the number of calls originating at peak time is 10, 000 in one hour, the calling rate is

A. 0.9
B. 10/9
C. 0.81
D. 0.1

Answer: Option B

Explanation:

Calling rate is the number of calls per subscriber.


20. 

If C is capacity of noisy channel, (bits/s), δf is bandwidth Hz and S/N is signal to noise ratio, then

A.
B.
C.
D.

Answer: Option A

Explanation:

This is Shannon-Hartley theorem.