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: <10720@accuvax.nwu.edu> Date: 11 Aug 90 09:11:42 GMT Sender: news@accuvax.nwu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 78 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 560, Message 2 of 3 "Dennis G. Rears (FSAC)" writes: > If only one line is installed in a jack why do the yellow and > black wires have to be attached? I suspect it doesn't. Generally that's true. In the olden days, the black/yellow sometimes served as the means to power the lamp in an old princess or trimline phone. In the REAL olden days, there was no black wire and the yellow wire was the ground, useful for party line service. > The modular jack that goes into the phone has four wires in it. Why > is that, if only the red and green are required for service? Just in > case you have a two line phone? This is one reason. Another would be for the A/A1 control for a key telephone system. If one adds a single line phone to a standard 1A2 key system, it must have a separate off-hook indication. > Why is the jack that goes from the telephone headset to the > telephone a different size than the jack that goes from the phone to > the wall jack? Is it to idiotproof the process? Also why four wires > into the headset? Does the phone itself do anything to the signals > before it sends it to the headset? If the proper size jack was put on > the headset could you plug that into the wall jack and recieve calls? Absolutely not. Believe it or not, all that stuff in the phone base actually serves a purpose. Besides the obvious, such as ringing and dialing, the base contains a "hybrid" circuit which takes the two wire phone line and converts it to a "four wire" circuit for the earpiece and for the tranmitter (microphone). It also provides a small DC polarizing voltage for the transmitter that is derived from the power in the phone line itself. Oh, and yes, the jacks are a different size for the purpose of idiotproofing. > What do the two wires (red and green or yellow and black) carry? Is > one postive and negative like electrical wires? Not LIKE electrical wires, they ARE electrical wires. Remember, electricity, not sound, travels through wires. Your voice is transformed into an electrical representation which is actually carried through the wires. > That says to me that there must be something physically > wrong with the Yellow or Black wires. That seems strange to me as all > four wires are in the same cable and if there was a physical break in the > cable it would affect all the wires, not just one or two. Any thoughts > of this? Long distance speculation of your problem would be difficult, but even if you get the line to work, you might want to replace the wiring with "twisted pair". The wire you describe, commonly called "D station wire" does not have the working pairs twisted. This almost invariably creates crosstalk between lines. Time and time again, there are people in this forum complaining about their modem line being heard in their voice line, etc., etc. The cause is usually traced to the fact that they are running two phone lines through D cable. What you want is "E wire", where the pairs are individually twisted. This often comes in three-pair and can be spotted by the colors: white/blue; white/orange; and white/green. I have E wire running all over the house, with modems, voice telephones, stations, and trunks all intermixed therein. There is no crosstalk whatsoever -- not a trace. Consider yourself lucky that there is something wrong with the D wire. Take the opportunity to pull it out and replace it with the right stuff: E wire. BTW, E wire comes "jacketed" and "unjacketed". Mine is all jacketed, but you can save a little money with unjacketed if it will run in a concealed place such as through the wall, in an attic, or under the house. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !