Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!ucbvax!jade!saturn!eshop From: eshop@saturn.ucsc.edu (Jim Warner) Newsgroups: comp.dcom.modems Subject: Re: What is Max speed possible on phone lines? Message-ID: <1070@saturn.ucsc.edu> Date: Mon, 2-Nov-87 16:18:19 EST Article-I.D.: saturn.1070 Posted: Mon Nov 2 16:18:19 1987 Date-Received: Fri, 6-Nov-87 23:48:05 EST References: <16064@topaz.rutgers.edu> <2174@kitty.UUCP> <138@ncc.UUCP> Reply-To: eshop@saturn.ucsc.edu (Jim Warner) Organization: University of California, Santa Cruz; CIS/CE Lines: 19 In article <138@ncc.UUCP> lyndon@ncc.UUCP (Lyndon Nerenberg) writes: >In article <2174@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes: >> >> The problem comes to pass when people buy these $ 25.00 balun >> transformers which match coaxial cable to balanced line, and run them over >> unshieled telephone pairs. The balun transformers themselves are just >> passive devices which need meet no FCC requirements of any kind; I can't >> envision their sale being "outlawed" or otherwise controlled. Questions of legality not withstanding, could someone explain how these things work? I thought Ethernet required low frequency response in order for collision detection to work. A collision is declared when the average voltage on the cable gets too negative. How do you get DC through a balun? On the other hand, if these are AUI (transciever cable) extensions, why would a balun be necessary at all? The impedance of phone wires isn't that far from the impedance of shielded twisted pairs, so what's to match?