Definition
A method of impressing information onto a radio carrier wave by varying the timing (phase) of the wave while leaving its amplitude and average frequency unchanged. The instantaneous shifts in phase represent the signal being transmitted.
Plain English
A way of carrying voice or data on a radio signal by slightly shifting the timing of each wave cycle instead of changing how strong or how fast the wave is.
Context Anchor
Seen in avionics, radio theory, and communication-system descriptions when explaining how information is placed onto a radio signal.
Derivation
Phase comes from the Greek phasis, meaning 'appearance' or 'stage'—here referring to the position of a wave at a given instant in its cycle. Modulation comes from the Latin modulare, 'to regulate' or 'to vary in measure.' Together: regulating the timing of the wave to carry information.
Why Pilots Care
Phase modulation is more resistant to noise than amplitude modulation, which is why it shows up in modern data links and some communication systems. Knowing the basic idea helps when reading avionics manuals or troubleshooting radio behavior.
Analogy
Think of a steady flashing light. If the flashes come just a little early or late to carry a message, the timing is being changed while the brightness stays the same.
Grounding Statement
Picture a steady wave rolling past at a fixed height and rate—now imagine nudging each cycle slightly earlier or later in time to spell out a message. The wave still looks the same in size and average speed, but the small timing shifts carry the information.
Intuition Check
Do not read phase modulation as a change in signal strength. The key change is timing: the wave is shifted ahead or behind in its cycle.
Example Sentence 1
The transmitter uses phase modulation to send digital data clearly even in noisy radio environments.
Example Sentence 2
Technicians check the phase modulation stage when troubleshooting intermittent radio static in the cockpit.