Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: John Higdon Newsgroups: comp.dcom.telecom Subject: Re: Basic Questions About Telephones Message-ID: <10760@accuvax.nwu.edu> Date: 12 Aug 90 18:41:32 GMT Sender: news@accuvax.nwu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 36 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 563, Message 4 of 12 On Aug 12 at 10:31, Roy Smith writes: > I am willing to defer to hard evidence to the contrary, but I have > trouble believing you could get any appreciable amount of crosstalk between > two properly balanced circuits (even if not using twisted pairs) over the, > say, 100 feet of wire you might find in a common residential installation. I have seen it happen over lengths of as little as 25 feet. Remember that crosstalk rejection between circuits depends on the electrostatic and electromagnetic cancellation caused by the two conductors of the circuit. If you have conductors randomly interspersed within a cable and if an individual leg of one circuit travel for some appreciable distance with the leg of another, then your "properly balanced circuits" might just as well be unbalanced. > My trailblazer coexists just fine with my voice line over plain old quad > wire, running what I would guess is about 60 feet in the same quad. In > theory, I would agree, you want to run twisted pairs if you have the > choice, but if quad is already in, I wouldn't bother replacing it for plain > voice or voice-grade modems. That's very nice. Random chance works in mysterious ways. The original poster indicated that there was some hard problem with his quad. Rather than nurse it back to health or replace it with more quad, my suggestion was to replace it with the "right stuff". I have a number of "cheap and dirty" tricks that I use and get away with, but don't don't usually advocate them in a public forum. The "I know it's wrong in theory, but it works fine for me" principle can cause people grief. Once again, I don't recommend using quad (or any non-twisted pair) cable for multiple lines. I have seen the results and they are bad. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !