Consider a carrier wave represented by
Here ec is instantaneous value, Ec is amplitude (maximum value), wc is angular frequency and q is the phase angle of carrier voltage.
Corresponding to the three variables Ec, wc and q, we can have three different types of modulation.
In this type if modulation, wc and q are kept constant. The amplitude Ec of the carrier wave is varied in accordance with the modulating wave.
In this type of modulation, Ec and q are kept constant. The frequency wc of the carrier wave is varied in accordance with the modulating wave.
In this type of modulation, Ec, wc are kept constant. The phase angle q of the carrier wave is varied according to the modulating wave. The common name for "phase modulation" and "frequency modulation" is "angle modulation".
