The maximum amplitude of an A.M. wave is found to be 15 V while its minimum amplitude is found to be 3 V. What is the modulation index?


Let the amplitude of the carrier signal be Ac and the amplitude of the message signal be Am.

Maximum amplitude, _______(1)


Minimum amplitude, _______(2)


Adding both the equations, we get




Subtracting (2) from (1), we get




The modulation index is given by:




Hence, the modulation index is 2/3.


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