Local oscillator
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A local oscillator is an electronic oscillator used to generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer. This process of frequency conversion, also referred to as heterodyning, produces the sum and difference frequencies of the frequency of the local oscillator and frequency of the input signal of interest. These are the beat frequencies. Normally the beat frequency is associated with the lower sideband, the difference between the two.
Several local oscillators can be strung in series to form a local oscillator chain (LO chain).
Local oscillators are used in the superheterodyne receiver, the most common type of radio receiver circuit. They are also used in many other communications circuits such as modems, cable television set top boxes, frequency division multiplexing systems used in telephone trunklines, microwave relay systems, telemetry systems, atomic clocks, radio telescopes, and military electronic countermeasure (antijamming) systems.