Which statement about Phase Modulation (PM) is true?

Which statement about Phase Modulation (PM) is true?

• A. PM is the same as Phase Shift Keying (PSK)
• B. PM modulates only frequency
• C. PM uses only amplitude
• D. PM has nothing to do with PSK

Answer: (A)

Phase modulation means the information is carried by changes in the carrier’s phase. Phase Shift Keying is a digital scheme that encodes data by changing the carrier phase among discrete values. Because PSK relies on phase changes to convey information, it is a form of phase modulation. In many discussions, PSK is treated as a specific, practical implementation of PM, so saying PM is the same as PSK captures that close relationship. The other statements don’t fit: PM does not modulate frequency (that’s frequency modulation) and it does not use only amplitude (that would be amplitude modulation). Also, PM is not unrelated to PSK—PSK is indeed a phase-modulation technique.

Phase modulation means the information is carried by changes in the carrier’s phase. Phase Shift Keying is a digital scheme that encodes data by changing the carrier phase among discrete values. Because PSK relies on phase changes to convey information, it is a form of phase modulation. In many discussions, PSK is treated as a specific, practical implementation of PM, so saying PM is the same as PSK captures that close relationship.

The other statements don’t fit: PM does not modulate frequency (that’s frequency modulation) and it does not use only amplitude (that would be amplitude modulation). Also, PM is not unrelated to PSK—PSK is indeed a phase-modulation technique.