From: utzoo!decvax!cca!hplabs!menlo70!sytek!zehntel!teklabs!keithe@sri-unix Newsgroups: net.music Title: On commercial-free FM Article-I.D.: teklabs.1299 Posted: Tue Jul 27 12:35:10 1982 Received: Thu Jul 29 04:33:59 1982 Commercial-free doesn't mean they have no source of income. There are the SCA channels (for Subsidiary Carrier Authorization, I think) which can be carried on standard FM signals which send other signals around; one of their (ab)uses is the Muzak (tm?) you hear in grocery stores, elevators and wherever. I think some paging-systems signals for doctors, computer technicians and other healers are also transmitted on these signals. Southwest Technical Products will sell you a kit to receive them - at least they used to - and it wasn't too expensive, either. But the musical quality of the signal is nothing to write home about, since it has to be bandlimited to prevent over-modulation problems. And it won't be in stereo. You can find stations broadcasting SCA in your area by using a spectrum analyzer (a Tektronix 7L12 or 7L13 will do just fine; so will some others but I don't know their model numbers) and observing the sidebands on the signals in the FM band. With some practice you'll be able to differentiate the L-R sidebands (which are at carrier +/- 38kHz) from SCA signals which will be located further away from the carrier. These sidebands are more easily distinguishable during periods of silence on the main channel. keith ericson at tektronix