# Analog Communications Questions and Answers – Costas Loop

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

1. Costa’s receiver is used for ________
a) coherent detection of AM-SC signal
b) asynchronous detection of AM-SC signal
c) amplification of signal
d) frequency mixing of signal

Explanation: A Costa’s loop is based on phase-locked loop (PLL). The circuit recovers carrier frequency from the suppressed-carrier modulated signals like DSBSC and SSBSC and phase modulated signals like FSK and BFSK. It is generally used for coherent detection of AM-SC signal in receivers.

2. Helical antenna is mainly used for ________
a) bandwidth calculation
b) production of video signals
d) satellite tracking

Explanation: A helical antenna is made of one or more conducting wires wound in the form of a helix. It is used for the communication (transmitting and receiving) Very High Frequency (VHF) signals through the different layers of atmosphere. Thus, it is used in satellite tracking.

3. Sampling frequency of a compact disk is about ________
a) 30 KHz
b) 50 KHz
c) 10 KHz
d) 70 KHz

Explanation: Sampling frequency is the number of samples per second which helps in extracting a discrete-time signal from a continuous-time signal. For a CD, it is about 10 KHz.

4. In frequency modulation, there is a large increase in noise and hence increase in the signal to noise ratio.
a) True
b) False

Explanation: In communication, Signal-To-Noise ratio (SNR) is defined as measure of the amount of signal present compared to the surrounding noise. It is the ratio of signal power to noise power. Thus, in frequency modulation, if there is a large decrease in noise, then there will be increase in the signal to noise ratio.

5. Image frequency is given by ________
a) fs + fi
b) fs ± fi
c) fs + 2fi
d) fs ± 2fi

Explanation: In the superheterodyne receiver, during the frequency conversion process, the local oscillator and the mixer often allow an undesired frequency signal, in addition to the incoming frequency signal. This results in the production of image frequency which is equal to the sum of signal frequency and double intermediate frequency.

6. Atmospheric noise, extraterrestrial noise and man-made noise is part of internal noise in communication.
a) True
b) False

Explanation: Atmospheric noise, extraterrestrial noise and man-made noise is part of external noise in communication. External noise are the ones which are produced by external sources, that are not part of the communication system. Internal noise are the ones which are produced by internal components of the communication system.

7. Thermal noise is a synonym of ________
a) Atmospheric noise
b) shot noise
c) Johnson noise
d) transit time noise

Explanation: Thermal noise is a type of internal noise in communication. It is produced due to thermal excitation of the free electrons in the circuit. It is also known as Johnson noise.

8. Distance at which a sky wave is received back on earth ________ with an angle of incidence.
a) increases
b) decreases
c) can be increase or decrease
d) can neither be increase or decrease

Explanation: The distance at which a sky wave is received back on earth is inversely proportional to the angle of incidence. Thus, the distance at which a sky wave is received back on earth decreases with an angle of incidence.

9. In a Vidicon camera tube, both sides of the target plate have the coating of Sno2.
a) True
b) False

Explanation: A vidicon camera tube is a type of camera tube having a photoconductive surface within. In Vidicon camera tube, the side of target plate facing the light has a coating of Sno2 and the side facing electron gun has a coating of antimony trisulphide.

10. Ground wave can be used for communication upto ________
a) 5 KHz
b) 12 KHz
c) 16 KHz
d) 25 KHz

Explanation: Ground wave is that wave that reaches a receiver from a transmitter directly without reflecting from ionosphere. It can be used for communication upto 16 KHz.

Sanfoundry Global Education & Learning Series – Analog Communications.

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