ObjectiveMcq
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In amplitude modulation, the modulation index m is kept less than or equal to 1 because:
Correct Answer: D — m > 1 indicates amplitude of message signal greater than amplitude of carrier signal, resulting in distortion.
The correct answer is D.
Concept:
The modulation index in AM is always kept less than 1 to avoid distortion or clipping of the message signal. When m > 1, the carrier undergoes a phase reversal of 180° and the envelope of the modulated signal no longer contains the actual message signal, resulting in a distorted output from the envelope detector.
Explanation:
When m > 1, the amplitude of the message signal exceeds the amplitude of the carrier signal.
This causes over-modulation, leading to envelope distortion where the envelope detector cannot faithfully recover the original message.
Additionally, m > 1 results in overlapping of both sidebands, causing loss of information.
Therefore, option D is the correct answer.