Phase Modulation (PM) involves what?

Phase Modulation (PM) involves what?

• A. Phase of carrier wave varied to transmit info
• B. Amplitude of carrier wave varied
• C. Frequency of carrier wave varied
• D. Data encoded as pulses

Answer: (A)

In phase modulation, the information is carried by changing the phase of the carrier wave over time. The carrier’s instantaneous phase is adjusted in proportion to the message signal, so the transmitted signal looks like s(t) = A cos(ωc t + kp m(t)). This means the same carrier amplitude stays constant while the angle on the complex plane shifts as the input data changes. That’s different from amplitude modulation, where the amplitude varies, and from frequency modulation, where the instantaneous frequency changes. Encodings that use pulses to represent data describe digital pulse schemes, not PM. So varying the phase of the carrier to transmit information is the defining idea of PM.

In phase modulation, the information is carried by changing the phase of the carrier wave over time. The carrier’s instantaneous phase is adjusted in proportion to the message signal, so the transmitted signal looks like s(t) = A cos(ωc t + kp m(t)). This means the same carrier amplitude stays constant while the angle on the complex plane shifts as the input data changes. That’s different from amplitude modulation, where the amplitude varies, and from frequency modulation, where the instantaneous frequency changes. Encodings that use pulses to represent data describe digital pulse schemes, not PM. So varying the phase of the carrier to transmit information is the defining idea of PM.