This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Superhetrodyne Receiver”.
1. Which of the following statement is true about frequency modulation?
a) noise gets decrease if we decrease deviation
b) noise gets decrease if we increase deviation
c) noise gets decrease by maintaining deviation constant
d) noise relates parabolically to deviation
View Answer
Explanation: In frequency modulated system, noise is inversely proportional to the frequency deviation. Thus, if we increase deviation then the noise in system gets decreases.
2. Colpitts oscillator is used in frequency modulation.
a) True
b) False
View Answer
Explanation: Crystal oscillator is used in frequency modulation to maintain a specific frequency with high stability overall.
3. The difference between phase and frequency modulation ________
a) lies in the poorer radio response of phase modulation index
b) lies in the different definition of modulation index
c) is too great to make the two systems compatible
d) is purely theoretical
View Answer
Explanation: It is the difference in definition of modulation index and also the general expression of the modulated wave that makes it different between phase and frequency modulated systems.
4. The frequency deviation is proportional to both amplitude and frequency in the phase modulated signal.
a) True
b) False
View Answer
Explanation: In phase modulation, the phase of the carrier signal is varied with respect to the amplitude of the message signal. For a phase modulated signal, the frequency deviation is proportional to amplitude only.
5. In a frequency modulated signal, the power _________ as the modulation index increases.
a) remains constant
b) increase
c) decrease
d) becomes 0
View Answer
Explanation: In a frequency modulated system, if we increase the modulation index the power remains constant as the power depends only on the amplitude of the message signal.
6. Frequency fogging is used to reduce noise in a carrier system.
a) True
b) False
View Answer
Explanation: Frequency fogging is used to cross talk in a carrier system.
7. Pre-emphasis circuit is used ________
a) before detection
b) after detection
c) before encoding
d) after encoding
View Answer
Explanation: Pre-emphasis is used in frequency modulated or phase modulated transmitters to equalize the drive power of transmitting signal in terms of deviation ratio. It is done at the transmitter. Its circuit is used before modulation.
8. De-emphasis circuit is used in circuit before detection.
a) True
b) False
View Answer
Explanation: De-emphasis means attenuating those frequencies by the amount by which they are boosted. De-emphasis is done at the receiver end i.e. it is used after detection. Detection refers to demodulation through which the original message signal is retrieved.
Sanfoundry Global Education & Learning Series – Analog Communications.
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