Exercise: Communication Systems

Questions for: Communication Systems

The discone antenna is
A:
used in UHF range
B:
circularly polarized
C:
used in radar
D:
used as a direction finding antenna
Answer: A

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

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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:
A:
1, 3, 4 are correct
B:
1 and 3 are correct
C:
2, 3, 4 are correct
D:
1, 2, 4 are correct
Answer: A

SWR is infinite if |rv| = 1.

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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?
A:
998 kHz
B:
999.7 kHz
C:
1000.3 kHz
D:
700 kHz
Answer: D

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

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In PCM, the information lies
A:
in one or two properties of the pulse
B:
in absence of pulse
C:
in presence of pulse
D:
in presence or absence of pulse
Answer: D

Depending on which logic is used.

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In a communication receiver, a squelch circuit is normally inserted
A:
before detector
B:
after detector
C:
before mixer
D:
after power amplifier
Answer: B

Squelch, i.e., muting is added after detector to suppress noise when no carrier is present at input.

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