Definition
An electronic oscillator circuit whose output frequency can be adjusted across a range, typically by varying the capacitance or inductance of a tuned circuit. In avionics, a variable-frequency oscillator is the tunable signal-generating stage inside radios and navigation receivers that lets the equipment be set to different operating frequencies.
Plain English
A circuit inside a radio that produces a steady electrical signal whose frequency can be changed. Turning the tuning knob on a radio adjusts this circuit so the radio operates on the chosen frequency.
Context Anchor
Seen in discussions of aircraft radios, navigation receivers, and avionics maintenance.
Derivation
From Latin oscillare, 'to swing.' An oscillator is a circuit that swings electrically back and forth at a steady rate. 'Variable-frequency' simply means that rate can be changed, rather than being fixed at one value.
Why Pilots Care
Allows a pilot or technician to select exact frequencies on legacy avionics without digital presets.
Analogy
It is like a whistle whose pitch can be changed. The whistle keeps making a steady sound, but you can adjust how high or low that sound is.
Intuition Check
“Variable” does not mean the frequency wanders randomly. Here it means the frequency is adjustable by design.
Example Sentence 1
The variable-frequency oscillator in the comm radio shifts to a new frequency each time the pilot dials in a different tower.
Example Sentence 2
During the preflight check the pilot noticed the comm radio would not hold frequency because the variable-frequency oscillator had drifted.