Heterodyne
From Wikinfo
In telecommunication, to heterodyne is to generate new frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, transistor, or diode mixer. The mixing of each two frequencies results in the creation of two new frequencies, one at the sum of the two frequencies mixed, and the other at their difference. A low frequency produced in this manner is sometimes referred to as a beat frequency. A beat frequency, or "beating," can be heard for example when multiple engines of an aircraft are running at close but not identical speeds.
A superheterodyne receiver converts any selected incoming frequency by heterodyne action to a preselected common intermediate frequency, for example, 455 kilohertz or 10.7 megahertz, and provides amplification and selectivity, or filtering.
The term heterodyne is sometimes also applied to one of the new frequencies produced by heterodyne signal mixing.
Heterodyning is not confined to electrical signals, but can occur in any medium where signals of different frequencies are mixed, such as sound vibrations in the aircraft engine example given above. A most unusual "in-brain" heterodyning of sterophonic sound is said to occur in the "Hemi-sync" process, which is claimed as an aid to astral projection.
See also
References
- Adapted from the Wikipedia article, "Heterodyne" http://en.wikipedia.org/wiki/Heterodyne, used under the GNU Free Documentation License
