Definition
A frequency produced when two signals of slightly different frequencies are combined in a nonlinear circuit. The beat frequency equals the difference between the two original frequencies and is used in radio receivers to convert incoming signals into a more usable form for amplification and detection.
Plain English
When two slightly different radio signals are mixed together, a new signal is created whose frequency equals the difference between the two. That new signal is the beat frequency.
Context Anchor
Seen in aircraft radio, navigation receiver, and avionics troubleshooting discussions.
Derivation
The word 'beat' comes from the audible pulsing or throbbing sound heard when two close-but-different musical tones are played together. The volume rises and falls at a rate equal to the difference between the two tones. Radio engineers borrowed the term because mixing two close radio frequencies produces the same kind of difference effect, just at radio rather than audio frequencies.
Why Pilots Care
Enables the pilot to hear and identify non-voice navigation or communication signals that would otherwise be silent.
Analogy
Think of two people humming notes that are slightly out of tune. You hear a slow 'wah-wah-wah' pulsing in the background. That pulsing rate is the beat frequency between their two voices.
Intuition Check
Beat frequency is not the average of two frequencies. It is the difference between them.
Example Sentence 1
The receiver mixes the incoming signal with a local oscillator to produce a beat frequency that is easier to amplify.
Example Sentence 2
A clear beat frequency tone confirmed the receiver was properly tuned to the unmodulated carrier.