Answer to Question #160343 in Electrical Engineering for Khushbu

Question

Why percentage modulation is always less than 100 % in case of A.M.?

Answer 1

The reason for this is in the definition of percent modulation: it is the ratio of peak voltage of modulating signal over peak voltage of unmodulated carrier multiplied by 100%:

$$m_\%=\frac{V_m}{V_c}\cdot100\%.$$

Percent modulation that exceeds 100% means that the modulating signal amplitude is greater than the carrier signal amplitude, which causes overmodulation and the signal becomes distorted. Thus, for amplitude modulation, the modulating signal amplitude must be smaller than the carrier peak voltage.