Phase modulation (1).

It is another type of angle modulation in which the phase of the carrier wave is changed according to the amplitude(magnitude) of the message (modulating) signal. In phase modulation, the amplitude of the carrier signal remains unchanged while phase change occurs. With change in phase, the frequency of the signal also shows variation. Thus it can be said that while phase modulating any signal, the phase as well as the the frequency of carrier signal, shows variation.