# 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

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

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

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

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.