This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “ Communication Systems – Detection of Amplitude Modulated Waves”.
1. What is the full form of IF?
a) Intermediate frequency
b) Internal frequency
c) Interval frequency
d) Immediate frequency
Explanation: Intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step during the transmission of a signal in order to facilitate further processing. In this, the carrier frequency is usually changed to a lower frequency preceding the detection.
2. Which of the following is not part of the detector system?
b) Envelope detector
d) AM wave
Explanation: The amplifier is a part of the receiver system, of which, the detector is a part of. But, the detector system alone consists of the rectifier, envelope detector, and obviously the amplitude-modulated wave that passes through it.
3. Which one of the following is the process of recovering the modulated signal?
Explanation: Detection is the process of recovering the modulating signal from the modulated carrier wave. The transmitted message gets attenuated in propagating through the channel. The receiving antenna is, therefore, to be followed by an amplifier and a detector. The detected signal may not be strong enough to be made use of and hence is required to be amplified.
4. The rectifier produces the output required in a communication system.
Explanation: Yes, this is a true statement. A rectifier converts alternating current (AC), which periodically reverses its direction, to direct current, which travels only in one direction. In a communication system, the modulated signal coming from the intermediate frequency (IF) stage is passed through the rectifier, located in the detector system, and the rectifier, in turn, produces the output required.
5. Which among the following can be detected by an envelope detector?
a) Low frequency AM waves
b) Very low frequency AM waves
c) Envelope detectors cannot detect AM waves
d) High frequency AM waves
Explanation: An envelope detector is used to detect high-frequency amplitude modulated (AM) waves. It takes high-level AM waves as input and then provides an output that can be considered as an envelope of the original signal. An envelope detector may consist of a simple RC circuit.
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