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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 7
31.
A 1000 kHz carrier is simultaneously modulated by 300 Hz and 2 kHz audio sine wave. Which of the following frequencies will not be present in the output?
998 kHz
999.7 kHz
1000.3 kHz
700 kHz
Answer: Option
Explanation:

1000 ± 0.3 and 1000 ± 2 kHz will be present.

32.
SWR for a transmission line is infinity when the load is
  1. Short circuit
  2. Complex impedance
  3. Open circuit
  4. Pure reactance
Of the above statements:
1, 3, 4 are correct
1 and 3 are correct
2, 3, 4 are correct
1, 2, 4 are correct
Answer: Option
Explanation:

SWR is infinite if |rv| = 1.

33.
The discone antenna is
used in UHF range
circularly polarized
used in radar
used as a direction finding antenna
Answer: Option
Explanation:

Discone antenna is a combination of disc and cone. It is omnidirectional and is used in VHF and UHF range especially at airports.

34.
The direction of pick up in a CD is
linear from centre towards edge
linear from edge to centre
nonlinear from centre to edge
nonlinear from edge to center
Answer: Option
Explanation:

It is linear from centre to edge.

35.
A (75 - j 50) Ω load is connected to a coaxial line of Z0 = 75 Ω at 10 GHz. The best method of matching consists of using
a capacitance at some specific distance from load
a short circuited stub at some specific distance from load
an inductance at load
a short circuited stub at load
Answer: Option
Explanation:

A short-circuited stub placed at a suitable distance from load provides best matching.

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