Exercise: Communication Systems

Questions for: Communication Systems

Which of the following is true in a tape recorder?
A:
Vow is due to variation in motor speed but flutter is due to some other reason
B:
Both vow and flutter are due to variations in motor speed
C:
Flutter is due to variation in motor speed but vow is due to some other reason
D:
Neither vow nor flutter is due to variation in motor speed
Answer: B

Small variation (less than 6%) in motor speed causes vow and large variation (more than 6%) in motor speed causes flutter.

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Consider the following reasons for using antenna coupler
  1. To prevent illegal radiation of spurious frequencies
  2. To tune out reactive components of antenna impedance
  3. To have correct value of load impedance for transmitter.
Which of the above are correct?
A:
1, 2, 3
B:
1, 2
C:
1 only
D:
2, 3
Answer: A

All the three are correct.

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A sinusoidal voltage of 2 kV peak value is amplitude modulated to give 20% modulation. The peak value of each side band term is
A:
400 V
B:
200 V
C:
100 V
D:
800 V
Answer: B

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A signal x(t) = 100 cos (24p x 103t) is ideally sampled with a sampling period of 50 μ sec and then passed through an ideal low pass filter with cut off frequency of 15 kHz Which of the following frequencies are present at the filter output?
A:
12 kHz only
B:
8 kHz only
C:
12 kHz and 9 kHz
D:
12 kHz and 8 kHz
Answer: D

Frequency pass by L.P.F. are, fc fs - fc

12 kHz, 8 kHz.

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When the carrier is unmodulated, a certain transmitter radiates 9 kW when the carrier is sinusoidally modulated the transmitter radiates 10.125 kW. The modulation index will be
A:
0.1
B:
10.15
C:
0.4
D:
0.5
Answer: D

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