This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Frequency Discrimination Method”.
1. FM and PM are two ways of angle modulation.
a) True
b) False
View Answer
Explanation: In angle modulation, phase or frequency of the carrier wave is varied with respect to the instantaneous amplitude of the message signal. The general expression for FM and PM are as follows:
FM (t) = Ac sin (2πfct + βsin(2πfmt)),
PM (t) = Ac sin (2πfct + βcos(2πfmt)), where symbols have their usual meaning.
2. FM transmitting and receiving equipment is __________ as compared to AM equipment.
a) costly
b) cheaper
c) same price
d) not available
View Answer
Explanation: Frequency transmitting and receiving equipment is generally costly when compared to amplitude modulated equipment.
3. Which one of the following is analog?
a) PCM
b) PWM
c) Delta modulation
d) Differential PCM
View Answer
Explanation: Frequency transmitting and receiving equipment are generally costly when compared to amplitude modulated equipment, as the power required in FM transmission is less and bandwidth is high. Also, the noise interference is also less in case of FM.
4. Schmitt trigger is used to generate PDM.
a) True
b) False
View Answer
Explanation: Pulse density modulation (PDM) is used to represent an analog signal using a digital signal. For generating PDM, a monostable multi-vibrator is used, which is externally triggered and has only one stable state.
5. Which of the following is used to generate PDM?
a) Monostable multi-vibrator
b) Bistable Multivibrator
c) Either monostable of free running multi-vibrator
d) Astable Multivibrator
View Answer
Explanation: Pulse density modulation (PDM) is used to represent an analog signal using a digital signal. For generating PDM, a monostable multi-vibrator is used, which is externally triggered and has only one stable state.
6. In case of FM, if the modulating frequency is lowered and the modulating voltage remains constant then the amplitude of distant sidebands decreases.
a) True
b) False
View Answer
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.
7. Skip distance depends on the time of day and angle of incidence.
a) True
b) False
View Answer
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.
8. Leak type bias is used in plate modulated amplifier to prevent tuned circuit damping.
a) True
b) False
View Answer
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.
9. For telegraphy pulse code modulation (PCM) is widely used.
a) True
b) False
View Answer
Explanation: FSK (Frequency Shift Keying) is a method used to transmit binary data in form of digital signals. It is mainly used for telegraphy. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for the communication between computers and over telephone lines.
10. DVD uses a laser beam for recording and video head for playback.
a) True
b) False
View Answer
Explanation: Digital Versatile Disc (DVD) uses a laser beam for both recording and playback.
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