Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: toddi@gtisqr.UUCP (Todd Inch) Newsgroups: comp.dcom.telecom Subject: Re: Two Lines From a Twisted Three? Message-ID: <1910@accuvax.nwu.edu> Date: 6 Dec 89 17:38:10 GMT Sender: news@accuvax.nwu.edu Reply-To: toddi@gtisqr.UUCP (Todd Inch) Organization: Global Technology International, Inc. Lines: 68 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 9, Issue 558, message 1 of 4 In article owens%tartarus@gargoyle.uchicago.edu (Christopher Owens) writes: >I want to bring a second phone line into my apartment . . . >Running from the terminal block to my apartment is an old-style >twisted-3 (conductor cable) . . . >From the junction box to my apartment is only a run of about 25 feet, >but the twisted three shares a conduit with two other twisted threes >serving two other apartments. >One thought was to use the extra wire of my three with an extra wire >taken from somewhere . . . I found out the hard way how important the "twisted pair" is: I once wired a building for phone using two "twisted-3" cables. My thought was that I wanted a total of six conductors, for up to three lines. What I really needed was a 3-pair equivalent, but at the time I didn't understand the "pair" concept. So I used one conductor from each cable to form the three pairs: {red A & red B}, {white A & white B}, {black A & black B}, where A is one twisted-3 cable and B is the other. This worked fine for the first line, but I had all the six conductor jacks installed before I connected the second line. That's when the trouble started. You could hear the conversations on the second line almost as well as you could hear your own conversation on the first, and vice-versa. Apparently, the twisting of the pair effectively sheilds it from the electromagnetic radiation of the other pairs. By not using any of the existing two twisted pairs but instead using separate twists for one wire of each line, I had created the worst-case condition, effectively creating a transformer which coupled the two lines together. The problem was especially bad because, at the time, my parents were going through a divorce and each had a separate phone line and they were sorta in separate buildings which shared some wiring. They didn't appreciate being forced to listen to each others' conversations. Anyway, if you try to use the spare conductor from your cable and the spare conductor from someone else's, you may end up with a three-way party line. It might work for only 25 feet, but I wouldn't bet on it. >I've been told there is a way to use some kind of bridge circuit at >each end of a 3-conductor wire to enable two phone lines to be run >over the wire. I once had a device on the outside of my house that allowed two different lines to somehow use the same pair to the phone company. Telco installed it and there must have been a device at the CO to run it. This was mentioned in passing here in the digest about a month ago. I'm not sure if you could convince telco to install one or not. Todd Inch, System Manager, Global Technology, Mukilteo WA (206) 742-9111 UUCP: {smart-host}!gtisqr!toddi ARPA: gtisqr!toddi@beaver.cs.washington.edu "You are the booger in the nose of my life." - My wife, to me. (Jokingly?) Disclaimer: My boss will read this while checking up on me and will disagree.