This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Singletone SSB Modulation”.
1. PDM can be generated by either free running multi-vibrator or monostable multi-vibrator.
Explanation: Pulse density modulation (PDM) is used to represent an analog signal using a digital signal. For generating PDM, monostable multi-vibrator is used, which is externally triggered and has only one stable state.
2. In case of FM, if the modulating frequency is lowered and the modulating voltage remains constant then the amplitude of distant sidebands first increases and then decreases.
Explanation: If the modulating frequency in FM lowered and the modulating voltage remains constant then the amplitude of distant sidebands increases, as the modulating frequency has no role to play in determining the amplitude of the sidebands.
3. Skip distance depends on the time of day.
Explanation: A skip distance is a distance between the point, where the radio waves from a transmitter are transmitted and the point where the waves are received, after having been refracted by different layers of the ionosphere. It basically depends on time of day as well as on angle of incidence.
4. Leak type bias is used in plate modulated amplifier to ________
a) increase bandwidth
b) decrease bandwidth
c) prevent tuning
d) prevent excessive grid current
Explanation: Leak bias is a type of bias in which the input signal draws grid current from a circuit made of resistors and capacitors. Thus, Leak bias is mainly used to prevent excessive grid current in plate modulated amplifiers.
5. Full duplex operation allows transmission in only one direction at the same time.
Explanation: Full duplex operations allow simultaneous communication between two points whereas Half Duplex operation allows transmission between two points one at a time.
6. A woofer is connected from the input through a ________
a) high pass filter
b) low pass filter
c) band pass filter
d) band stop filter
Explanation: A woofer is connected from the input through a low pass filter to restrict the high frequencies and only allows the low frequencies to pass through it.
7. Which of the following is used for attenuating high frequencies?
a) shunt resistance
b) shunt inductance
c) series capacitance
d) shunt capacitance
Explanation: Shunt capacitance is used to improve the power factor in the network. It also improves voltage stability. It serves as a low pass filter and thus is used in the communication system for attenuating high frequencies.
8. If the length of antenna is equal to whole wavelength the radiation is zero in all direction.
Explanation: If the length of antenna is equal to whole wavelength only the radiations which is at right angles is zero.
9. For getting zero radiation at right angles, length of antenna should be __________
Explanation: For getting zero radiation at right angles, length of antenna should be equal to the whole wavelength.
10. What is the commercial frequency deviation of frequency modulation?
a) 70 KHz
b) 75 KHz
c) 80 KHz
d) 85 KHz
Explanation: Frequency deviation is the difference between the maximum instantaneous modulated frequency and carrier frequency. Frequencies lying nearly about 75KHz is considered as commercial frequency deviation for frequency modulation.
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