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

1. The output stage in a television transmitter is likely to be ________
a) screen modulated
b) plate modulated
c) rectangular modulated
d) grid modulated

Explanation: We generally use vestigial sideband modulation (VSB) for television production as it reduces the required bandwidth. However, the output stage in a television transmitter is generally grid modulated using a Class C amplifier, In grid modulation, the carrier wave to the message signal is provided by the grid circuit of the electron tube.

2. The advantage of using mechanical filter in filter system of sideband suppression is good band pass.
a) True
b) False

Explanation: Generally, the filters have sharp cut-off frequency as a result of which either of the sidebands are not completely suppressed. Thus, the advantage of using mechanical filter in filter system of sideband suppression is smaller size, good band pass and good attenuation characteristics.

3. Television transmission is possible through ________
a) DSB-SC
b) SSB-SC
c) VSB
d) AM

Explanation: We generally use vestigial sideband (VSB) for television production. In VSB, one of the sidebands is completely transmitted whereas the other sideband is partly transmitted, along with the carrier. VSB is used as it reduces the required bandwidth to half.

4. The rms value of a thermal noise voltage is proportional to (where k is Boltzmann’s constant) _______
a) √k
b) k
c) k2
d) k13

Explanation: Thermal noise is the noise generated in electronic devices at frequencies below a few kilohertz, due to thermal excitation of electrons. The root mean square value of thermal noise is proportional to root k times, where k represents Boltzmann’s constant.

5. For a human eye the minimum viewing angle of resolution should be ʎD where D is iris opening and ʎ is wavelength of light.
a) True
b) False

Explanation: For a human eye the minimum viewing angle of resolution should be 1.22ʎ/D. The diameter of human eye is about 25mm.
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6. In amplitude modulation, magnitude of side bands is ________ times the carrier amplitude.
a) ma2
b) 4ma
c) ma
d) 2ma

Explanation: In amplitude modulation, for a good transmission and reception, the magnitude of side bands must be 4ma times the amplitude of carrier wave, (where, m = Modulation Index and a = Amplitude of Message signal).

7. Noises which get generated within the receiver is called ________
a) Internal noise
b) External noise
d) Extraterrestrial noise

Explanation: Internal noise in communication is the noise that gets generated within the receiver or communication system.

8. Autocorrelation function of white noise is ________
a) an impulse function
b) a step function
c) a constant
d) a variable

Explanation: White noise is an internal noise of communication system having different frequencies present with equal intensities. It has a peak only at zero and are zero at all points. Thus, the autocorrelation function of white noise is a constant.

9. In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno2 (tin oxide) and the side facing electron gun has a coating of antimony trisulphide.
a) True
b) False

Explanation: A vidicon camera tube is a type of camera having a photoconductive surface within. In a 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. Marconi antenna ________
a) is a grounded antenna
b) is an ungrounded antenna
c) can either be grounded or ungrounded antenna
d) can neither be grounded nor ungrounded antenna

Explanation: Marconi antenna is like a vertical wire having length one fourth of the working wavelength. Thus, it is a quarter wave monopole antenna. Since it was invented by Guglielmo Marconi, so it’s also called Marconi Antenna. It requires a ground plane with very good conductivity. Hence it is also called as a grounded antenna.

Sanfoundry Global Education & Learning Series – Analog Communications.

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