Electronics and Communication Engineering - Communication Systems

16.
In radar systems PRF stands for
Power Return Factor
Pulse Return Factor
Pulse Repetition Frequency
Pulse Response Factor
Answer: Option
Explanation:

PRF in radar systems means pulse repetition frequency.


17.
Which of the following cannot be the Fourier series expansion of a periodic signal?
x(t) = 2 cos t + 3 cos 3t
x(t) = 2 cos pt + 7 cos t
x(t) = cos t + 0.5
x(t) = 2 cos 1.5pt + sin 3.5 pt
Answer: Option
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?
Reactance bipolar transistor modulator
Armstrong modulator
Varactor diode modulator
Reactance FM modulator
Answer: Option
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
0.9
10/9
0.81
0.1
Answer: Option
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
Answer: Option
Explanation:

This is Shannon-Hartley theorem.