Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!netsys!vector!telecom-gateway From: desnoyer@apple.com (Peter Desnoyers) Newsgroups: comp.dcom.telecom Subject: Re: Praise the Lord and Pass the RF Filters Message-ID: Date: 26 Jun 89 17:06:38 GMT Sender: news@vector.Dallas.TX.US Organization: Apple Computer, Inc. Lines: 30 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 215, message 1 of 8 In article goldstein@delni.enet.dec.com (Fred R. Goldstein dtn226-7388) writes: > Any nonlinear element > will rectify the signal, "detecting" AM transmissions, whose transmitted > power varies (in the time domain) in accordance with the modulation. > [...] > But an FM station? Not so fast. FM transmitters maintain a constant > amplitude, so if you "detect" them with a simple rectifier, you won't > get anything but perhaps a steady DC voltage. Not so fast again - to detect AM you only need a non-linear element; to detect FM you need a non-linear element combined with a frequency response that is not flat at the frequency being detected. Seeing as telephony equipment is designed for audio frequencies, it should have a pretty steep roll-off at 100MHz. The oxide on any connector will provide a small non-linearity, and the high field strength should make up for the huge inefficiencies involved. (I once had a poorly shielded turntable that would receive WBCN in Boston from an MIT dorm - I know it was BCN because it would come in clear enough that you could hear the DJ. One of the connectors from the turntable had broken, and I had screwed up the shielding when I replaced it. Of course, there's a world of difference between interfering with a magnetic pick-up signal at 10-20 mV into 47k ohms and interfering with a telephone signal of perhaps 500-1000 mV into 600 ohms.) Peter Desnoyers Apple ATG (408) 974-4469