Text: The term originally applied by Fessenden to a method of reception of electromagnetic waves wherein the principle of Beats (q.v.) was employed. It is derived from the words "hetero," meaning other or different, and "dyne," meaning power. In its original conception by Fessenden before the widespread use of vacuum tubes, it was used in conjunction with crystal receivers for the reception of undamped waves. The heterodyne principle involves production of a local series of oscillations which are tuned to a frequency differing from the frequency of the incoming oscillations from the antenna. The difference between the two is known as the beat frequency.

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