Analog Communication questions for Placement
1. A CW transmitter radiates
(A) Unmodulated RF carrier
(B) Modulated RF carrier
Answer: A
2. In SSB the pilot carrier is provided
(A) For stabilizing frequency
(B) To reduce noise
(C) For reducing power consumption
(D) As an auxiliary source of power
ANSWER: A
3. In the standard AM radio broadcast band, the frequency tolerance for the RF
carrier is
(A) Zero
(B) +25 Hz
(C) + 20 Hz
(D) +1000 Hz
ANSWER: C
4. If a 900 KHz carrier is amplitude modulated with a 4000Hz audio tone the lower
and upper frequencies are
(A) 800 and 1000 KHz
(B) 450 and 1800 KHz
(C) 4000 and 8000 KHz
(D) 896 and 904 KHz
ANSWER: D
5. In an AM signal, the peak antenna current = 12 A, the minimum antenna current =
3A. The percentage modulation is
(A) 60 %
(B) 100 %
(C) 50 %
(D) 40 %
ANSWER: A
6. High-level modulation is used in a 5 KW AM transmitter. For 100% modulation the
value of audio signal power needed is
(A) 2.5KW
(B) 0.5KW
(C) 1KW
(D) 1.5KW
ANSWER: A
7. What will be the overall modulation when a carrier is simultaneously modulated by
two sine waves of modulation indices 0.8 and 0.6?
(A) 0.5
(B) 1.0
(C) 0.7
(D) 0.9
ANSWER: B
8. Consider a transmitter that radiates 9kW when the carrier is unmodulated. When
the carrier is sinusoidally modulated a transmitter radiates 10.125 KW. What will
be the modulation index?
(A) 50%
(B) 40%
(C) 60%
(D) 100%
ANSWER: A
9. During amplitude modulation, the phase angle of the modulating voltage changes by
(A) 180°
(B) 90°
(C) 45°
(D) 0°
ANSWER: D
10. A FM discriminator changes
(A) FM signal into AM signal
(B) FM signal into PM signal
(C) FM signal into FM signal of high frequency
(D) FM signal into FM signal of low frequency
ANSWER: A
11. In an FM transmitter, the final power amplifier usually operates as
(A) Class A
(B) Class B
(C) Class C
(D) Class D
ANSWER: C
12. In FM broadcasting the frequency of the stereo sub-carrier signal is
(A) 48KHz
(B) 78KHz
(C) 19KHz
(D) 38KHz
ANSWER: D
13. Let noise phase-modulates the FM Wave. As noise side band approaches the carrier
frequency, the noise amplitude
(A) Is decreased
(B) Is increased
(C) Is equalized
ANSWER: A
14. Foster seelay discriminator uses a
(A) Single tuned circuit
(B) Double tuned circuit with primary and secondary tuned to the different frequency
(C) Double tuned circuit with primary and secondary tuned to the same frequency
ANSWER: C
15. A narrow band FM can be approximated to __________ when bandwidth is the
major consideration
(A) SSB
(B) FM
(C) AM
ANSWER: C
16. Bandwidth of a FM wave is 160 KHz and modulation index is 7.5. The frequency
deviation is
(A) 75MHz
(B) 75KHz
(C) 16KHz
(D) 16MHz
ANSWER: B
17. FM is indirectly generated by
(A) Armstrong modulator
(B) Hartley oscillator
(C) Varactor diode modulator
(D) Transistor modulator
ANSWER: A
18. For a FM broadcast station the assigned carrier frequency is 99.7 MHz. Its FM
signal has a rest frequency of
(A) 99.7 MHz
(B) 99.7 KHz
(C) 99.7 Hz
(D) 100 MHz
ANSWER: A
19. Consider a case where frequency doubler has an FM signal input at 13 MHz with a
deviation of 5KHz.The output frequency for the carrier will be
(A) 26.1 MHz
(B) 10KHz
(C) 100 MHz
(D) 26 MHz
ANSWER: D
20. The ratio of time on to time off in pulse transmitter is called
(A) Bandwidth
(B) Duty cycle
(C) Efficiency
(D) Base
ANSWER: B
21. To transmit normal speech signal, bandwidth required in the PCM channel is
(A) 4 KHz
(B) 2 KHz
(C) 8 KHz
(D) 64 KHz
ANSWER: D
22. To generate PWM signal the technique used is
(A) Differentiating the PPM signal
(B) Integrating the PPM signal
(C) A astable multivibrator is used
(D) A monostable multivibrator
ANSWER: A
23. De-emphasis circuit is used
(A) After modulation
(B) Prior to modulation
(C) For de-emphasizing low frequency component
(D) For de-emphasizing high frequency component
ANSWER: D
24. A balanced modulator produces
(A) SSB
(B) AM
(C) VSB
(D) DSB
ANSWER: D
25. Two waveforms are 180° out of phase. What will be the beat frequency at 276 MHz?
(A) 2.76 MHz
(B) 276 KHz
(C) 455 KHz
(D) Zero
ANSWER: D
26. The frequency of local oscillator in a superheterodyne receiver is
(A) Equal to incoming signal
(B) Higher than incoming signal
(C) Less than incoming signal
ANSWER: B
27. Consider a super heterodyne receiver with no RF amplifier. The loaded Q of the antenna
coupling circuit at the input of the mixer is 100. The intermediate frequency is 445 KHz.
At 1000KHz the image frequency will be
(A) 1910KHz
(B) 1000KHz
(C) 455KHz
(D) 2000KHz
ANSWER: A
28. Consider a super heterodyne receiver with no RF amplifier. The loaded Q of the antenna
coupling circuit at the input of the mixer is 100. The intermediate frequency is 445 KHz.
At 100 KHz the rejection ratio will be
(A) 39.5
(B) 100
(C) 138.6
(D) 80.2
ANSWER: C
29. Consider an AM radio with IF = 455KHz. The oscillator frequency for tuning in 710
KHz is
(A) 1000 KHz
(B) 255 KHz
(C) 150.5 KHz
(D) 1165 KHz
ANSWER: D
30. Through a mixer when an FM signal with a deviation d is passed its frequency is
reduced five fold. The deviation in the output of the mixer is
(A) Indeterminate
(B) 5d
(C) d
(D) d/5
ANSWER: D
