Definition
An electronic oscillator circuit that generates a continuous sine-wave signal at a specific frequency, using a tuned tank circuit made up of a tapped inductor (or two inductors in series) and a single capacitor, with feedback taken from the tap on the inductor to sustain oscillation.
Plain English
A circuit that produces a steady radio-frequency signal. It does this by combining a coil and a capacitor that resonate at one chosen frequency, with a small portion of the coil's signal fed back into the circuit to keep the signal going.
Context Anchor
Seen in aircraft radio, navigation, and avionics theory when discussing how electronic equipment creates or controls signal frequencies.
Derivation
Named after Ralph Hartley, the American electronics engineer who invented and patented the circuit in 1915 while working at Western Electric. The name simply identifies the inventor, but knowing it is a named circuit (not a descriptive term) helps when reading avionics texts that reference several oscillator types by their inventors -- Hartley, Colpitts, Clapp.
Why Pilots Care
Pilots normally do not adjust or troubleshoot a Hartley oscillator in flight, but understanding the term helps when reading about how radios and other avionics create stable signals.
Analogy
A tuned coil-and-capacitor pair acts like a pendulum that naturally swings at one rate. The feedback from the inductor tap is the small push that keeps the pendulum swinging steadily instead of dying out.
Intuition Check
Do not picture a mechanical part shaking back and forth. In this term, oscillator means an electronic circuit producing a repeating electrical signal.
Example Sentence 1
The technician traced the radio's signal-generation problem to a failed component in the Hartley oscillator stage.
Example Sentence 2
Early transceivers relied on a Hartley oscillator to maintain a steady transmitting frequency.