Which of the following is a result of over-modulation?

In AM modulation, the modulation index 'or' modulation depth (m) is defined as a measure of the extent to which a carrier voltage is varied by the modulating signal.

It is one of the key parameters whose value determines if there is a distortion in the AM signal or not.

It is evaluated mathematically as:

\(μ=\frac{A_m}{A_c}\)

For three different values of modulation index, we have different output waveforms as:

Under Modulation (μ < 1):

Critical Modulation (μ = 1):

Over Modulation (μ > 1):

Observation:

• As the value of the modulation index increases, the carrier experiences a 180° phase reversal, which causes additional sidebands, and hence, the wave gets distorted.
• Such an overmodulated wave causes interference, which cannot be eliminated.