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From: duncan@bolero.ati.com (James R. Duncan)
Newsgroups: sci.electronics
Subject: Re: SCA Tuner
Message-ID: <29953@bolero.ati.com>
Date: 14 Apr 91 23:34:43 GMT
References: <1991Apr12.195637.25132@uncecs.edu> <12780002@hpuplca.nsr.hp.com>
Reply-To: duncan@bolero.ati.com (James R. Duncan)
Organization: KUFX 94.5 FM Stereo, San Jose, CA "The Fox"
Lines: 26

In article <12780002@hpuplca.nsr.hp.com> jeff@hpuplca.nsr.hp.com (   Jeff Gruszynski  ) writes:
>	Primary SCA is an FM signal @ 67KHz w/ 15KHz Max Deviation sitting 
>above (frequency wise) the 38KHz L-R DSB signal.  I seem to remember *old* 
>National Semiconductor Linear databooks having an SCA application example 
>on the LM565 entry.  I also seem to remember SCA being covered by the ECPA.
>(i.e. You're not supposed to listen).  Anyone with a better memory out
>there?
>
Nowadays any workable combination of "SCA" subcarrier channels can be
inserted above the 38 kHz L-R DSB subcarrier.  This would take the form
of data and/or analog audio channels with center frequencies from 60 to
110 kHz depending on the application.  The LM565 is a cheap but
perfectly adequate detector for SCA. It will provide a cleaner output
if preceded by a filter. 

"You're not supposed to listen" because the SCA messages (Muzak, data,
or whatever) generally haven't been cleared for home use.  Nobody seems
to really care until you decode a Muzak background music channel and
then play it throughout your retail store without paying for the
service, etc., etc..   

-- 
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