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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 8
1.
In a satellite system circular polarization is to be obtained. The antenna used is
parabolic
horn
log periodic
helical
Answer: Option
Explanation:

Helical antenna produces a circularly polarized radiation if its two components are at right angles and are equal. It is very commonly used in radio telemetry.

2.
A horizontal output stage is cutoff for retrace and 40% of trace. If time for each horizontal line is 64 μs and retrace time is 12 μs, the transistor is conducting for about
64 μs
6.4 μs
31 μs
3.1 μs
Answer: Option
Explanation:

Total time for each horizontal line = .

Time for trace = 64 - 12 = 52 μs.

Time for which transistor is not conducting = 12 + 0.4 x 52 = 32.8 ms.

Time for which transistor is conducting = 64 - 32.8 = 31 μs.

3.
A TV remote control works on the principle of
pulse code modulated ultra violet light
pulse code modulated infrared light
demodulation
either (a) or (b)
Answer: Option
Explanation:

Infrared light is used in TV remote control.

4.
As the magnitude of reverse bias is increased, the capacitance of varactor diode
increases
decreases
first increase, then decreases
first decreases then increases
Answer: Option
Explanation:

When magnitude of reverse bias is increased, thickness of depletion layer increases.

Capacitance is inversely proportional to thickness.

5.
To prevent overloading in the last IF amplifier one should use
variable sensitivity
squelch
double conversion
variable selectivity
Answer: Option
Explanation:

Variable sensitivity prevents overloading.

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