# Analog Communications Questions and Answers – Linear Modulation

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

1. Discone antenna is mainly used in UHF range.
a) True
b) False

Explanation: A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath. Discone antenna is a combination of disc and cone. Discone antenna is omnidirectional so it is mainly used in UHF range. It is especially used in airports.

2. Squelch circuit is normally inserted in receiver ________
a) after detector
b) before detector
c) before mixer
d) after power amplifier

Explanation: Squelch is a circuit that acts to suppress the audio (or video) output of a receiver in the absence of a sufficiently strong desired input signal. Squelch is added to suppress noise. It is added after detector when there is no carrier.

3. Each frequency gives rise to four side bands.
a) True
b) False

Explanation: Each frequency in communication gives rise to two side bands, Upper Sideband and Lower Sideband.

4. Field strength (E) is directly proportional to the square of transmission power.
a) True
b) False

Explanation: Field Strength is the intensity of an electric or magnetic field. Actually the Field strength (E) is directly proportional to the square root of transmission power i.e. E ∝ √Pt.

5. If the transmitted power is 100KW then the field at a distance ‘R’ is 60mV/m. Suppose if the transmitted power is reduced to 50KW then the field at same distance ‘R’ will be equal to ________
a) 50mV/m
b) 42mV/m
c) 45mV/m
d) 55mV/m

6. If the value of resistor becomes 16 times than its previous value then its noise voltage will become ________
a) 16 times
b) 8 times
c) 4 times
d) 2 times

Explanation: Since the noise voltage is directly proportional to square root of resistance so if the value of resistor increased to 16 times then its noise voltage will become 4 times.

7. What is the modulation index for a single tone modulation, given that positive peak of AM wave is 20V and minimum value is 2V?
a) 0.81
b) 0.91
c) 0.73
d) 1

Explanation: Modulation Index (u) = (Vmax – Vmin)/(Vmax + Vmin)
= (20-2)/(20+2) = 9/11 = 0.81.

8. TV remote control used ultra violet light.
a) True
b) False

Explanation: The infrared (IR) and the ultraviolet(UV) rays represent the two extremities of the visible spectrum (400-700nm). While IR represents electromagnetic radiation with wavelengths longer than those of visible light, UV represents wavelengths shorter than visible light. Each time we press any button of TV remote, it sends a beam of infrared rays. For different commands, it sends out different beams that are detected by a microchip lying inside TV.

9. How capacitance is related to thickness?
a) it is inversely proportional to thickness
b) it is directly proportional to thickness
c) it is inversely proportional to twice of thickness
d) it is directly proportional to twice of thickness

Explanation: The thickness of capacitor affects the value of capacitance because capacitance is dependent on structure and distance between two plates.
Thus, Capacitance, C = A×∈t so it is inversely proportional to thickness.

10. Noise gets mixed with signal at ________
b) transmitter
c) transducer
d) channel

Explanation: Channel acts as a path for taking signals to the receiver. It is a medium of transmission of data from source to destination. There is a high probability of involving noise at the channel.

Sanfoundry Global Education & Learning Series – Analog Communications.

To practice all areas of Analog Communications, here is complete set of 1000+ Multiple Choice Questions and Answers. 