Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: Julian Macassey Newsgroups: comp.dcom.telecom Subject: Re: Crosstalk on Two lines on One Four-Wire Cable Message-ID: <11885@accuvax.nwu.edu> Date: 7 Sep 90 12:56:34 GMT Sender: news@accuvax.nwu.edu Organization: The Hole in the Wall Hollywood California U.S.A. Lines: 64 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 629, Message 1 of 12 In article <11734@accuvax.nwu.edu>, libove@lemans.det.dec.com (Jay Libove) writes: > Well, I have two phone lines - one voice, one data - on a four wire > typical phone line, and I experience crosstalk that I believe might > actually occasionally interfere with my data communications, and is > always annoying (to both parties) on the voice line. > Do I have any legal right to make the phone company come in and > correct a situation that they caused? They knew before doing the > second line "installation" (just plug in a two-jack plate and split > the wires, $75, on top of $40 'line charge' !!!) that the line was to > be used for data communication. Legally, the Telco gave you what you asked for, a second line connected to a jack. For $50.00 you could have got a freelance to do it right. It's quad vs. twisted pair time again. Most domestic installations use cable that has a white plastic jacket. This cable has four wires inside. The four wires make up "two pairs". The first pair, the wires that carry the first line, are the Red and Green. Most telephone wire, like the wire going all the way back to the CO (exchange) is what is known as twisted pair. It is twisted so as to remain balanced to ground and null out induced signals. You can lay hundreds of twisted pairs next to each other with no crosstalk problems. None of the above refers to quad. Quad is not twisted. Using quad can give rise to cross talk. The longer the quad run, the greater the chance of cross talk. One "Okie fix" to quad cross talk is use a separate piece of quad cable for each line rather than use the Yellow and Black second pair. The best thing to do is rip out all quad and install "Three Pair". This stuff uses a different colour code: white/blue-blue/white, white/orange-orange/white, white/green-green/white. This job is easy to do. Three pair is cheap, you can get 1,000 Feet for about $40.00 (Your milage may vary). The jacket of twisted pair is usually "artificial limb pink" which is for some reason called "beige", it is available in "designer grey", I have seen some black jacketed twisted pair. The drop wire. This is the overhead cable that brings the line into some domestic installations. If it is a single line drop, the wire is not twisted. It is also flying through the air so is not liable to suffer from crosstalk. Multi-line drop wire, six pairs etc, is twisted pair. All the underground subscriber feeds I have seen use twisted pair. So it is very simple, want clean quiet lines? Use twisted pair. The Telco will usually use quad in domestic and single line installs. Installers are often happy to use twisted pair if you ask for them. But, you don't have to get the Telco to do your inside wiring, you can do it yourself or pay anyone else to do it. The Telco has priced themselves out of the inside wiring biz and their standards seemed to have slipped post divestiture. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495