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Definition: phase modulation

Varying the angle of a wave in a carrier in order to transmit analog or digital data. For digital signals, phase modulation (PM) is widely used in conjunction with amplitude modulation (AM). For example, quadrature amplitude modulation (QAM) uses both phase and amplitude modulation to create different binary states for transmission (see QAM). See modulation and carrier.

Vary the Angle
In PM modulation, the angle of the carrier wave is varied by the incoming signal. In this example, the modulating wave implies an analog signal.

Digital Phase Shift Keying (PSK)
For digital signals, phase shift keying (PSK) uses two phases for 0 and 1 as in this example. See DPSK.