What is Phase Modulation (PM)?

What is Phase Modulation (PM)?

• A. A form of modulation that represents information as variations in the instantaneous phase of a carrier wave.
• B. A modulation method that varies amplitude with time.
• C. A technique that changes the frequency of the carrier without phase variation.
• D. A method of encoding data using pulse positions.

Answer: (A)

Phase modulation encodes information by changing the instantaneous phase of the carrier, rather than its amplitude or its frequency. In PM, the modulating signal controls the phase deviation of the carrier, so the instantaneous phase φ(t) shifts in proportion to the input signal while the carrier’s amplitude stays essentially constant. The result is a waveform whose phase variation contains the information to be transmitted. This contrasts with amplitude modulation, where the information is carried by changes in amplitude; with frequency modulation, where the instantaneous frequency changes; and with pulse-position modulation, where the data are conveyed by the timing of pulses. PM is also related to techniques like PSK, where discrete phase changes encode symbols.

Phase modulation encodes information by changing the instantaneous phase of the carrier, rather than its amplitude or its frequency. In PM, the modulating signal controls the phase deviation of the carrier, so the instantaneous phase φ(t) shifts in proportion to the input signal while the carrier’s amplitude stays essentially constant. The result is a waveform whose phase variation contains the information to be transmitted. This contrasts with amplitude modulation, where the information is carried by changes in amplitude; with frequency modulation, where the instantaneous frequency changes; and with pulse-position modulation, where the data are conveyed by the timing of pulses. PM is also related to techniques like PSK, where discrete phase changes encode symbols.