Angle modulation

Angle modulation is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is respectively based on altering the frequency or the phase of a carrier signal to encode the message signal. This contrasts with varying the amplitude of the carrier, practiced in amplitude modulation (AM) transmission, the earliest of the major modulation methods used widely in early radio broadcasting.

In general form, an analog modulation process of a sinusoidal carrier wave may be described by the following equation:

Here, A(t) represents the time-varying amplitude of the sinusoidal carrier wave and the cosine-term is the carrier at its circular frequency ${\displaystyle \omega }$, and the instantaneous phase deviation ${\displaystyle \phi (t)}$. This description directly provides the two major groups of modulation, amplitude modulation and angle modulation. In amplitude modulation, the angle term is held constant, while in angle modulation the term A(t) is constant and the second term of the equation has a functional relationship to the modulating message signal.

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