Angle Modulation
Angle modulation varies the angle of a carrier wave according to the amplitude of the modulating baseband signal (the message signal). The amplitude of the carrier is kept constant. Phase modulation and frequency modulation are particular types of angle modulation.
Angle modulation can be expressed using the following equation:
where
Ac is the carrier amplitude
fc is the carrier frequency
kf is the frequency deviation constant in Hz/V
fm is the frequency of the message signal