Xref: utzoo sci.electronics:6158 rec.ham-radio:10717 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!snjsn1!bilbo!greg From: greg@bilbo (Greg Wageman) Newsgroups: sci.electronics,rec.ham-radio Subject: Re: Need frequency information for microwave transmitter Message-ID: <955@snjsn1.SJ.ATE.SLB.COM> Date: 9 May 89 19:01:37 GMT References: <5847@brspyr1.BRS.Com> Sender: news@SJ.ATE.SLB.COM Reply-To: greg@sj.ate.slb.com (Greg Wageman) Distribution: na Organization: Schlumberger ATE, San Jose, CA Lines: 36 In article <5847@brspyr1.BRS.Com> miket@brspyr1.BRS.Com (Mike Trout) writes: > >The chip used is a TI TX8835 N 96856. It is connected to a 9-dipswitch unit >with 3 positions per switch. I'm assuming that this allows certain pins on the >chip to be placed high, low, or neutral. As there are thousands of possible >combinations, I have no way of finding out what the possible frequencies for >this chip may be. This is admittedly just a guess, but is based on knowledge of my own garage-door transmitter. The dipswitches probably don't alter the frequency at all, but control some sort of code modulated onto the carrier. This is supposed to provide greater security and prevent a would-be-thief from simply driving up to your house and blasting selected frequencies at your garage until the door opens, or simply carrying a number of common door-opener transmitters and trying them until one works (don't laugh, it happens). The number of possible codes in my case is 2^10 (1024), since there are 10 dipswitches. The frequency is most likely determined by a crystal oscillator. There's probably a tuning coil with a powdered-iron slug for tweaking it, although not all designs have this. Some only have fixed inductors and a small trimmer capacitor for matching with the printed circuit loop "antenna". Longish .signature follows. Skip now, or don't complain. Greg Wageman DOMAIN: greg@sj.ate.slb.com Schlumberger Technologies UUCP: ...!uunet!sjsca4!greg 1601 Technology Drive BIX: gwage San Jose, CA 95110-1397 CIS: 74016,352 (408) 437-5198 GEnie: G.WAGEMAN ------------------ "Live Free; Die Anyway." ------------------ Opinions expressed herein are solely the responsibility of the author.