On Wed, 30 Mar 2005, Vern Jones wrote:

> 38Khz is the suppressed carrier for the upper side bands for stereo
> demodulation associated with Stereo FM radio. The 38 Khz demodulation
> carrier is suppressed, so there is only the upper and lower sidebands of the
> L-R signal, to decode this part of the stereo transmission the 38Khz carrier
> must be regenerated. This regeneration is derived from a 19 Khz signal
> transmitted along with the FM broadcast transmission. Normally a phase
> locked loop is used to regenerate the 38 Khz. Look up the LM1800 to see how
> the 38 Khz is regenerated for Stereo Demodulation for a FM Stereo Signal.

And more to the point, 18kHz crystals made for this exist but are rare 
and expensive. They are about 3 inches long ;-)

Peter
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