crisp@uncecs.edu (Russ Crisp) (04/13/91)
Hello all. I'm interested in building an SCA tuner to browse through this service on FM broadcast stations in my area. Anyone know of a kit or an article that would get me going on this? Thanks! Russ Crisp KA4UXZ Western Carolina University
jeff@hpuplca.nsr.hp.com ( Jeff Gruszynski ) (04/13/91)
/ hpuplca:sci.electronics / crisp@uncecs.edu (Russ Crisp) / 12:56 pm Apr 12, 1991 / * Hello all. * * I'm interested in building an SCA tuner to browse through this * service on FM broadcast stations in my area. Anyone know of * a kit or an article that would get me going on this? * * Thanks! * Russ Crisp KA4UXZ * Western Carolina University * ---------- 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? Jeff Gruszynski Santa Clara Sales Hewlett-Packard
duncan@bolero.ati.com (James R. Duncan) (04/15/91)
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.. -- KUFX | w ["] | WA6MBV 94.5 |.. |___|_____..duncan@bolero.ati.com | Jim Duncan FM | H | +1 408 297 5977 \_____I_____/ 37 3 10N/121 59 10W ---------------
reichert@motcid.UUCP (Chuck KD9JQ) (04/16/91)
The 38Khz L-R info is part of the 0-15Khz L+R Audio info. 19Khz 10% Pilot is doubled to 38Khz and suppressed (DSB). The 67Khz is all by itself and usually some sort of PLL detection is required. Use of a stereo decoder chip LM-1800, 2800, etc.) with the de-emphasis removed and the output fed to the PLL (CD 4046, etc) decoder has worked in the past. Chuck Reichert KD9JQ
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (04/16/91)
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? Actually, it's illegal under the ECPA to listen to any subcarriers, because they are encrypted communications. I suppose this goes for SCA services. It also applies to television audio and to FM stereo, so I think that we can all get together and agree that the ECPA is worthless and unenforceable. In a more happy vein, the latest Signetics Linear databook also has an SCA decoder as one of the example circuits listed for one of their PLL detectors. It would also be fairly easy to use one of the FM stereo decoder chips to do it, by using a tank circuit tuned to 38 instead of 19 KC. Anyone need some pentagrid converters? --scott