# Analog Communications Questions and Answers – AGC

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

1. Standard intermediate frequency used for AM receiver is ________
a) 455 MHz
b) 455 KHz
c) 455 Hz
d) 20 KHz

Explanation: Standard intermediate frequency (IF) used for AM receiver is 455KHz. IF is obtained by mixing the incoming siganl frequency with the locally generated signal frequency in order to convert the incoming RF signal frequency to a low frequency which can be processed easily.

2. Which device is used in TV receivers for tuning the receiver to the incoming signal?
a) Varacter diode
b) High pass filter
c) Low pass filter
d) Bandpass filter

Explanation: Varacter diodes have variable capacitance as a function of variable input voltage. It works in reverse bias. It is generally used for tuning the receivers according to an incoming signal. It is also used in RF filters for tuning purposes such as tuning of TV sets.

3. What is the bandwidth occupied by a DSB signal when the modulating frequency lies in the range from 100Hz to 10KHz?
a) 19.8 KHz
b) 19.8 Hz
c) 19.8 MHz
d) 19.8 GHz

Explanation: According to given problem, fm = fmax-fmin = 10KHz – 100Hz = 10000 – 100
= 9900Hz. Therefore bandwidth is equal to 2fm = 2 X 9900 = 19.8 KHz.

4. Which statement is true about multiplexing?
a) it is used to reduce the bandwidth
b) it is used to combine multiple data streams over a single data channel
c) it is used to allow multiple data streams over multiple channels
d) it is used to match and pass the same frequency signal

Explanation: Multiplexing is a process where multiple data streams from different sources are combined and transmitted over a single data channel. It is placed at the transmitting end to combine the signals.

5. What is the noise figure of merit for an SSB modulated signal?
a) less than 1
b) greater than 1
c) 1
d) 0.5

Explanation: Figure of merit is the ratio of output signal to noise ratio to input signal to noise ratio of a receiver system, oftenly used to describe the performance of a system. Figure of merit for SSB modulation is always 1.
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6. Which amplifier is preferably used for low level modulation?
a) Class C
b) Class A
c) Class AB
d) Class B

Explanation: We called a modulation as low level when the modulation takes place prior to the output element of the final stage of the amplifier at low power. Class A amplifiers are used for this purpose.

7. If a receiver has a poor capacity of blocking adjacent channel interference then the receiver has ________
a) Poor selectivity
b) Poor Signal to Noise ratio
c) Poor sensitivity
d) Poor fidelity

Explanation: Selectivity is used to separate out closely lying components in terms of frequency. If the receiver has poor selectivity then it also has a poor capacity of blocking adjacent channel interference.

8. What is the advantage of using a VSB transmission?
a) Higher bandwidth than SSB
b) Less power required as compared to DSB-SC
c) Lower bandwidth than SSB
d) Both higher bandwidth than SSB and less power required as compared to DSB-SC

Explanation: Vestigial Side Band is similar to single sideband (SSB) transmission, in which the second sideband is not completely removed, but is filtered to remove the range of frequencies that are not required. It has higher bandwidth than SSB-SC and less power consumption than DSB-SC.

9. What is the value of modulation index m, for overmodulation?
a) m < 1
b) m = 1
c) m > 1
d) m = 0

Explanation: When the modulation index m is greater than 1 i.e. m > 1 it is called overmodulation. It generates modulation with distortions and overlapping in the envelope of the modulated signal which makes it difficult to recover the information.

Sanfoundry Global Education & Learning Series – Analog Communications.

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