Difference Between Frequency Modulation and Phase Modulation:

The Difference Between Frequency Modulation and Phase Modulation are discussed below

FM and PM are quite similar except by the manner in which the modulation index is defined.

1. For FM, the phase angle is proportional to modulating wave whereas for PM, the time derivative of phase angle is proportional to modulating wave.

2. In FM, the frequency deviation is proportional to the amplitude of the modulating signal whereas in PM, the phase deviation is proportional to the amplitude of the modulating signal and, therefore, independent of its frequency.

3. In case of FM, the modulation index is inversely proportional to the modulating frequency whereas in PM, the modulation index is proportional to the modulating voltage.

It means that under identical conditions FM and PM are indistinguishable for a single modulating frequency. When the modulating frequency is changed, the PM modulation index will remain constant but the FM modulation index will decrease as modulating frequency is increased and vice versa.