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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 3
31.
If D is mouth diameter of a paraboloid reflector, its directivity is proportional to
D
D2
D
D3
Answer: Option
Explanation:

Directivity of parabolic reflector = .

32.
A noiseless 3 kHz channel can't transmit binary bit at the rate
12000 bps
1000 bps
6000 bps
3000 bps
Answer: Option
Explanation:

Noiseless channel: Nyquist's Theorem - If the signal has V discrete levels over a transmission medium of bandwidth H, the maximum data rate = 2H log2 V bits/sec.

A noiseless 3-kHz channel cannot transmit binary signals at a rate exceeding 6000 bps (= 2 x 3000 log2 2).

33.
In an AM wave the carrier and one of the side bands is suppressed. If m = 1, the percentage saving in power is
25%
50%
66.6%
83.3%
Answer: Option
Explanation:

.

34.

Assertion (A): An electronic tuner uses varactor diode

Reason (R): The capacitance of a varactor diode depends on the magnitude of reverse bias.

Both A and R are correct and R is correct explanation of A
Both A and R are correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Answer: Option
Explanation:

A varactor diode has a variable capacitance which depends on reverse bias. It is a very convenient device for tuning.

35.
A superheterodyne receiver is to operate in the frequency range 550 kHz - 1650 kHz, with the intermediate frequency of 450 kHz. Let denote the required capacitance ratio of the local oscillator and I denote the image frequency (in kHz) of the incoming signal. If the receiver is tuned to 700 kHz, then
R = 4.41 J =1600
R = 2.10 J =1150
R = 3.0 J =1600
R = 9.0 J =1150
Answer: Option
Explanation:

Image frequency = 700 + 2 x 450 1600 kHz

fmax = 1650 + 450 2100 kHz

fmin = 550 kHz + 450 1000 kHz

R = 4.41, I = 1600 kHz.

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