Definition
A condition in an electronic circuit in which a local oscillator is held in a fixed phase relationship with an incoming reference signal. A phase-locked loop (PLL) compares the phase of the two signals and continuously adjusts the local oscillator so it stays synchronized with the reference.
Plain English
A circuit technique that keeps one signal perfectly in step with another. The circuit constantly watches the incoming signal and nudges its own signal to match, so the two stay locked together.
Context Anchor
Seen in avionics, radio, navigation receiver, and electronic instrument discussions.
Derivation
Phase refers to the timing position of a wave in its cycle. Lock means held firmly in place. Together: the timing of one wave is held firmly in step with another.
Why Pilots Care
Phase-lock circuits are what allow modern radios and nav receivers to tune precisely to a chosen frequency and hold it without drift. Stable communications, accurate VOR signals, and reliable GPS tracking all depend on phase-lock working correctly.
Analogy
Think of two metronomes on the same shelf: when one is tapped to match the other, they begin ticking together and stay together. Phase lock is the electronic version of that.
Intuition Check
Lock does not mean a physical latch here. It means an electronic signal has been synchronized and is being held in step with another signal.
Example Sentence 1
The avionics technician confirmed the receiver had achieved phase lock before testing the navigation output.
Example Sentence 2
A momentary loss of phase lock caused the indicator to flicker until the signal stabilized again.