Question

If modulation index is greater than 1
(A) The baseband signal is not preserved in the envelope of the AM signal
(B) The recovered signal is distorted
(C) It is called over modulation
(D) All of the above

Answer 1

Hint
The modulation index of a carrier signal measures the extent up to which the modulated variable of the carrier signal varies about its unmodulated level. When the value of the modulation index goes more than one then it causes overmodulation which leads to distortion and causes the bandwidth to not be preserved.

Complete step by step answer
The modulation index is the amount of modulation that is done on a carrier signal. It can be defined as the ratio of the peak voltage of the modulating signal and the peak voltage of the carrier signal.
When we have a modulation index of value greater than 1, say $1.5$ then the modulating signal has a greater amplitude which causes part of the information to get lost in the process of modulation. This is termed as overmodulation.
So option (C). is correct.
The resulting waveform contains gaps that show that the information got lost. So the recovered signal is always distorted. Hence, option B. is also correct.
And as there is a loss of data, the message will be damaged, which will damage the signal's effectiveness, strength, and quality. Therefore, the bandwidth signal is not preserved in the envelope of the AM signal.
Hence, option (A). is also correct.
Therefore, the correct answer will be option (D) as all the given options are correct.

Note
The term modulation index can be used to define several forms of modulation and for a different form of modulation there are different methods to obtain the modulation index.
When the modulation signal goes above 1, the carrier signal experiences $180^\circ $ phase reversal which gives rise to additional sidebands. These sidebands cause serious interference and distortion.