Path: utzoo!telecom-request Date: 23 Apr 91 14:54:09 GMT From: oberman@ptavv.llnl.gov Newsgroups: comp.dcom.telecom Subject: Re: Radio Reception on Telephone Message-ID: Organization: TELECOM Digest Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 301, Message 4 of 10 Lines: 29 In article , hpa@casbah.acns.nwu.edu (H. Peter Anvin) writes: > Well, a "choke" is a fairly simple device consisting mainly of > capacitors and inductors and the purpouse of which is to short out the > RF radiation before it gets detected in your phone. It can be > effective sometimes, and totally worthless at times. Well, a "choke" is not "a fairly simple device consisting mainly of capacitors and inductors". That's a filter, also commonly called a trap. A choke is simply an inductor which is, in turn, simply a coil. Coils work because they present an impedence which increases with frequency. And you want to block RFI while allowing in audio. I'm not familiar with the impedences in telephones, but I suspect that a 10 mH inductor should do the trick. It would present a 63 K impedence at 1 MHz. Frankly a little PI filter made of two chokes and a capacitor would work better, but just a choke will probably do the job. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything. Especially anything gnu.