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Analog Communications Multiple Choice Questions focuses on “Noise for AM Wave”.
1. The image frequency of a superheterodyne receiver ___________
a) is created within the receiver itself
b) is due to insufficient adjacent channel rejection
c) is not rejected by the IF tuned circuits
d) is independent of the frequency to which the receiver is tuned
Answer: c
Clarification: To eliminate the image frequency of a superheterodyne receiver, adequate attenuation on the incoming signal by the RF amplifier filter is needed. It is not rejected by the IF tuned circuits and thus, it produces image frequency.
2. Which one of the following circuits could not demodulate SSB?
a) Phase Shift Method
b) Filter Method
c) Weaver Demodulator
d) Phase discriminator
Answer: d
Clarification: Phase discriminator cannot be used to demodulate SSB. It is used to discriminate between different phases.
3. Which of the following statement is true about a radio detector?
a) the linearity is worse than in phase discriminator
b) there is stabilization against signal strength variations
c) the final output is twice of that obtainable from a similar phase discriminator
d) the circuit is same as in a discriminator, except that the diodes are reversed.
Answer: a
Clarification: Detector, also known as a demodulator, in a radio receiver extracts the original information that is contained in a modulated radio wave. The linearity of a radio detector is worse than in phase discriminator. However, the radio detector does not get affected by amplitude variations and minimizes the limiting required.
4. To prevent overloading of the IF amplifier in a receiver, one should use _________
a) squelch
b) variable selectivity
c) double conversion
d) variable sensitivity
Answer: a
Clarification: Squelch is a circuit that is preferably used to prevent overloading of the IF amplifier in a receiver.
5. In a broadcast superheterodyne receiver, the ____________
a) Local oscillator always operates below the frequency of transmitted signal
b) Input of mixer must be tuned to the signal frequency
c) Local oscillator frequency should be double than that of IF
d) RF amplifier normally works at 455 KHz above the carrier frequency
Answer: b
Clarification: For a superheterodyne receiver, one of the inputs of the mixer must be tuned to the signal frequency and another input is of the local oscillator frequency. Tuning means that the circuit works for that one signal frequency only.
6. Which of the following statement is false regarding Armstrong modulation system?
a) The system is basically phase modulated and not frequency modulated
b) Automatic Frequency Control (AFC) is not needed as a crystal oscillator is used
c) Frequency multiplication must be used
d) Equalization is necessary
Answer: d
Clarification: The Armstrong method generates a double sideband carrier signal, phase shifts this signal and then reinserts the carrier to produce a frequency modulated signal. In Armstrong modulation system equalization is not necessary.
7. If the target cross section is changing, the best system for accurate tracking is __________
a) sequential switching
b) lobe switching
c) conical scanning
d) monopulse radar
Answer: d
Clarification: Monopulse radar compares the received signal from a single radar pulse against itself in order to compare the signal in various aspects. If the target cross section is changing then it is the best system used for accurate tracking.
8. After a target has been acquired, the best scanning system for tracking is _________
a) circular
b) spiral
c) conical
d) helical
Answer: c
Clarification: Conical is the best scanning system for tracking. But it is only preferred for tracking after a target has been acquired.
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