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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 5
16.
AM amplifier having noise figure of 20 dB and available power gain of 15 dB is followed by a mixer circuit having noise figure of 9 dB. The overall noise figure as referred to input in dB is
10.44
11.07
21.52
0.63
Answer: Option
Explanation:

.

17.
Which one of the following is non-resonant antenna?
Folded dipole
Broad side array
End fire array
Rhombic antenna
Answer: Option
Explanation:

Rhombic antenna is a non-resonant antenna capable of operating over 3 to 30 MHz range.

18.
If the oscillator output is modulated by audio frequencies upto 10 kHz, the frequency range occupied by the side bands will be
711.9 kHz to 712.1 kHz
702 kHz to 722 kHz
692 kHz to 732 kHz
71.2 kHz to 71.20 kHz
Answer: Option
Explanation:

Sideband frequencies will be fc ± fm.

19.
The efficiency of using a binary system for selection of 1 out of 13 equally probable events is
100%
about 92%
about 83%
about 71%
Answer: Option
Explanation:

log2 13 = 3.7 therefore, number of bits = 4.

.

20.
The most suitable method for detecting a modulated signal g(t) = (3 to 6 cos 2pfmt) cos 2pfct is
envelope detector
synchronous detector
ratio detector
both a and b
Answer: Option
Explanation:

Because it is an AM envelope.

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