Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!ucselx!bionet!hayes.ims.alaska.edu!floyd
From: floyd@hayes.ims.alaska.edu (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Noisy phone lines
Message-ID: <1990Nov20.131818.28875@hayes.ims.alaska.edu>
Date: 20 Nov 90 13:18:18 GMT
References: <1990Nov15.193826.3875@beach.csulb.edu> <2983@hayes.uucp> <1546@westmark.WESTMARK.COM>
Organization: University of Alaska Fairbanks
Lines: 46

In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes:
>In article <2983@hayes.uucp>, tnixon@hayes.uucp (Toby Nixon) writes:
>
>> Remember -- as soon as that phone cable leaves your house, it 
>> immediately goes into a big fat cable with literally hundreds or 
>> thousands of other pairs of copper wire.  If "crosstalk" was going 
>> to be a problem, you'd have already run into it!!
>
>No, not exactly.  The big fat cable has individual twisted pairs
>which are all twisted in such as way as to cancel the crosstalk
>which would otherwise be created by induction between them.

I'm not clear on what you meant by "all twisted", so here is a
little more:
Each pair is twisted.  Other than that the only placement or
arrangement done is to make it easy to identifiy which is which.

>The original question was concerned with running two voice-frequency
>circuits (one of which happened to be used by a modem) in the same
>piece of quad.  Quad has four wires, with no twists, and no
>anti-crosstalk arrangement.  Crosstalk does occur in such cables,
>but it doesn't become noticable until the cable length approaches a
>hundred feet or so. (An admittedly subjective measurement ... your
>mileage may vary.)

Agreed on the distance and the variation.  

What I do wonder about is what kind of quad this is that is not
twisted.  I don't work with cpe or outside plant other than my own
home.  But the stuff I buy at radio shack is twisted pair (3 pair, not
quad) and the quad jk we use on PBX extentions at work is twisted pair.
I really can't imagine running inhouse cabling that is not twisted
pair.  We sure don't put anything on a distribution frame longer than
about 6 inches that is not twisted pair (it has to be on the same
block, or it is twisted pair).

Take a look at some of that non-twisted quad and see if it doesn't
really have a twist about every 1-2 feet.

Floyd


-- 
Floyd L. Davidson                             floyd@hayes.ims.alaska.edu
Salcha, AK 99714                    paycheck connection to Alascom, Inc.
 When I speak for them, one of us will be *out* of business in a hurry.