Angle modulation

Angle modulation is the generic term for phase angle modulation and frequency modulation.

Angle modulation types are modulation types in which the instantaneous phase angle of the carrier is influenced by the signal to be transmitted.

In the phase modulation of the relative phase angle of the carrier is affected by the instantaneous value of the signal voltage. At the frequency of modulation, the frequency of the carrier is affected by the instantaneous value of the signal voltage.

The instantaneous frequency of the carrier corresponds to the time derivative of the phase angle.

In frequency modulation, the high frequencies of a useful signal can be transmitted worse, since the phase shift with increasing signal frequency is smaller. To counteract the correspondingly higher signal to noise ratio after the modulator is used in FM radio to a pre-emphasis in the transmitter on the useful signal. This pre-emphasis is reversed with a de-emphasis in the receiver.

For phase modulation, the low frequencies can be transmitted less as the frequency change of the carrier signal is proportional to the signal frequency, and therefore is only a slight change in the carrier frequency at low signal frequencies.