Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!bloom-beacon!athena.mit.edu!eichin From: eichin@athena.mit.edu (Mark W. Eichin) Newsgroups: sci.electronics Subject: Re: Jamming supermarket music systems (was: Jamming Walkmans) Message-ID: <1909@bloom-beacon.MIT.EDU> Date: Sun, 29-Nov-87 07:50:16 EST Article-I.D.: bloom-be.1909 Posted: Sun Nov 29 07:50:16 1987 Date-Received: Tue, 1-Dec-87 05:55:04 EST References: <4149@utai.UUCP> <1160@uhccux.UUCP> <3810@bellcore.bellcore.com> Sender: daemon@bloom-beacon.MIT.EDU Reply-To: eichin@athena.mit.edu (Mark W. Eichin) Organization: Many Intoxicated Topologists Lines: 32 The subcarrier systems (under the tradename StoreCast) are a 38KHz subcarrier off of an FM broadcast station (19KHz is for the L-R signal.) Thus, anything that can interfere with normal FM transmission should do the job here; note that it would be equally illegal.[1] A StoreCast receiver can be built with only slight modifications to any `well-built' FM stereo unit, I even purchased a kit somewhere that had an extra amplifier stage that you could tap into your FM unit to receive such broadcasts, with the reminder that you cannot use the gadget in a commercial manner. If you were to build such a jammer, wouldn't you need so much power that it would freak the electronic cash registers, if you got too close? FCC Class A & B regard emissions, not absorption; the last REALLY shielded machine I saw was the IBM 9000[2] `lab workstation' which was this 68K based un!x box that could be safely run next to an induction furnace... Actually, TEMPEST requirements deal with that, I suspect, if you can find someone to tell you :-) Mark Eichin[1] Speculation: a walkman(tm) jammer that simply induced a signal in the headphones directly would probably not be illegal, because of the (presumeably) low power needed? You can generate alot of EMF in a 5 foot antenna wire... [2] I saw this 4-5 years ago at an IBM demo in CT somewhere, in a division that may not exist anymore; I may have the number wrong. Reply by mail if you want more specifics on what I think I saw. Disclaimer: I think these are my opinions, but don't quote me on it ;-)