Heterodyne

Heterodyne comes from the Greek root hetero-"different" and -dyne"power".

In radio and signal processing, heterodyne is the generation of new frequencies by mixing or multiplying two oscillating waveforms. It is useful for modulation and demodulation of signals, or placing information of interest into a useful frequency range.

Mixing two frequencies creates two new frequencies, one at the sum of the two frequencies mixed, and the other at their difference. Typically only one of these frequencies is desired--the higher one after modulation and the lower one after demodulation. The other signal is either not passed by the tuned circuitry follows or may be filtered out.