This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Noise for DSB-SC”.
1. The discone antenna is ________
a) useful direction-finding antenna
b) used as a radar receiving antenna
c) circularly polarized
d) useful as VHF and UHF receiving antenna
Explanation: A discone antenna is almost same as a biconical antenna in which one of the cones is replaced by a disc. It is mounted vertically, with the disc at top and cone beneath. It is useful as UHF and VHF receiving antenna.
2. Which one of the following is not an omnidirectional antenna?
d) Half-wave dipole
Explanation: Omnidirectional antenna radiates radio wave power uniformly in all directions in one plane. From above given antennas, log-periodic antenna is not an omnidirectional antenna.
3. If the value of a resistor creating thermal noise is doubled. The noise power generator is therefore ________
Explanation: If the value of resistor creating thermal noise is doubled then also the noise power generator remains unaffected, since the two are independent of each other.
4. Which one of the following is not a useful quantity for comparing the noise performance of receivers?
a) Input noise voltage
b) Signal To Noise Ration
c) Noise Figure
d) Figure of merit
Explanation: Noise performance of different receivers cannot be compared on the basis of input noise voltage. It can be calculated on the basis of figure of merit, or noise figure, or on the basis of equivalent noise resistance.
5. Which of the following is the most generally used term for comparing amplifier noise characteristics?
a) signal to noise ratio
b) equivalent noise
c) noise factor
d) figure of merit
Explanation: Noise factor measures degradation of signal to noise ratio which is caused by components in radio frequency (RF) signal chain. It is a number by which the performance of an amplifier can be specified, with lower values indicating better performance.
6. The number of lines per field in the United States TV system is _________
Explanation: The number of lines per field in the United States TV system is 262.5.
7. The number of frames per second in the United States TV system is _________
Explanation: The number of frames per second in the United States TV system is 30.
8. Why interlacing is used in television?
a) to reduce noise in video signals
b) to ensure that all the lines on screen are scanned
c) to reduce the disturbances
d) to avoid flicker
Explanation: Interlacing is used for doubling the perceived frame rate of a video display without consuming the extra bandwidth. It is mostly used in television to avoid flicker.
9. The signals sent by the TV transmitters to ensure correct scanning in the receiver are called luminance.
Explanation: The signals sent by the TV transmitters to ensure correct scanning in the receiver are called sync. Luminance refers to the component of television which carries information on the brightness of the image. It refers to the intensity of the screen.
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