Exercise: Communication Systems

Questions for: Communication Systems

A carrier is phase modulated (PM) with frequency deviation of 10 kHz by a single tone frequency of 1 kHz. If the single tone frequency is increased to 2 kHz, assuming that phase deviation remains unchanged, the bandwidth of the PM signal is
A:
21 kHz
B:
22 kHz
C:
42 kHz
D:
44 kHz
Answer: D

Frequency deviation = 10 kHz, fm = 1 kHz

2(fm + Df)

Bandwidth = 22 kHz

2(10 + 1) 22 kHz

fm is doubled

Hence 22 x 2 44 kHz bandwidth.

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Compact discs use
A:
magnetic recording and retrieval
B:
optical recording and retrieval
C:
optical recording but magnetic retrieval
D:
magnetic recording but optical retrieval
Answer: B

CD uses optical recording and retrieval.

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Which of the following are useful in comparing the noise performance of receivers?
  1. Input noise voltage
  2. Noise figure
  3. Noise resistance
  4. Noise temperature
Select answer as per the following codes:
A:
1, 2 and 3
B:
1, 3 and 4
C:
2, 3, 4
D:
1, 2, 4
Answer: C

Noise figure, noise resistance and noise temperature are useful quantities. Input noise voltage alone is not sufficient unless gain of amplifier stages is also known.

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In a satellite transponder the power amplifier feeds power P to the transmitting antenna of gain G. If distance of earth is d, the power flux density is
A:
PG/d
B:
PG/4pd2
C:
P/G(4pd2)
D:
Answer: B

Available power is PG and is spread over 4 nd2.

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In Vidicon camera tube, the resistance of photoconductive material on the target plate
A:
is constant
B:
is more in darkness and less in brightness
C:
is more in brightness but less in darkness and brightness
D:
may be more or less in darkness and brightness
Answer: B

Light dependent resistor (LDR) has high resistance in darkness and low resistance in brightness.

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