# Analog Communications Questions and Answers – Frequency Domain Representation

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This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Frequency Domain Representation”.

1. The spectrum of white noise and impulse noise is similar in terms of ________
a) magnitude spectrum
b) phase spectrum
c) both magnitude spectrum and phase spectrum
d) amplitude spectrum

Explanation: White noise is a random signal having equal intensities of different frequencies. Impulse noise is a type of noise consisting of sudden sounds, which includes unwanted and instantaneous signals. Thus, they have only their magnitude in common.

2. The amount of power and bandwidth necessary to be transmitted for a given amount of information are reduced in _________
a) Single Sideband Modulation
b) Double Sideband Modulation
c) Vestigial Sideband Modulation
d) Amplitude Modulation

Explanation: In SSBSC, the carrier is suppressed and only either of the two sidebands is transmitted. This reduces the power consumption and also lessens the bandwidth. While in DSBSC, the carrier is suppressed but both the sidebands are transmitted, whereas in AM, the carrier as well as both the sidebands are transmitted.

3. A long wave AM broadcast transmitter needs _________
a) very small carrier power
b) very large carrier power
c) small carrier power
d) large carrier power

Explanation: In Communication Systems, a transmitter produces radio waves, which are the modulated message signals, and are transmitted via the antennae. These message signals carry information which are modulated using a carrier wave, having frequency higher than the message signal frequency. Thus, for transmitting information to a large distance, it is necessary that a very large carrier wave is used for modulation.

4. In FM, if we decreases modulating frequency then the modulation index ________
a) will increase, if the modulating voltage amplitude increases
b) will decrease, if the modulating voltage amplitude increases
c) will increase, if the modulating voltage amplitude remains constant
d) will decrease, if the modulating voltage amplitude remains constant

Explanation: In frequency modulation, the modulation index is the ratio of frequency deviation to modulating frequency. Therefore, modulation index can be made inversely proportional to the modulating frequency by keeping amplitude constant. Thus, if we decrease modulating frequency then the modulation index will increase, with amplitude remaining constant.

5. Which of the following modulation system is used for video-modulation?
a) DSB-SC
b) SSB-SC
c) VSB
d) FM

Explanation: Vestigial Sideband Modulation (VSB) is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. Thus, video signals are transmitted using VSB modulation.
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6. In SSB modulation, only a single sideband is transmitted leaving the other sideband and the carrier.
a) True
b) False

Explanation: In SSBSC, the carrier is suppressed and only either of the two sidebands is transmitted. This reduces power consumption and also lessens the bandwidth.

7. For demodulation of PCM, it is first converted into __________
a) PDM
b) PWM
c) PPM
d) PAM

Explanation: Pulse Code Modulation deals with converting an analog signal to a digital signal. During it’s demodulation, the wave to be treated is to be parallel. The series pulse wave signal is then converted into a parallel digital signal using a serial to parallel converter, after which it is further converted into the original analog signal with the help of a decoder or detector.

8. A noise can be represented as superposition of spectral components.
a) True
b) False

Explanation: Noise is any undesirable electrical energy that falls under the passband of the signal. It is a general term for the unwanted signals that gets added to our original signal. It is usually represented as the superposition of spectral components.

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