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From: wb8foz@mthvax.cs.miami.edu (David Lesher,,255RTFM,255rtfm)
Newsgroups: comp.dcom.modems
Subject: Twisted pairs, was: Noisy phone lines
Message-ID: <1990Nov21.003204.6372@mthvax.cs.miami.edu>
Date: 21 Nov 90 00:32:04 GMT
References: <1990Nov15.193826.3875@beach.csulb.edu> <2983@hayes.uucp> <1546@westmark.WESTMARK.COM> <1990Nov20.131818.28875@hayes.ims.alaska.edu>
Reply-To: wb8foz@mthvax.cs.miami.edu (David Lesher)
Distribution: na
Organization: NRK Clinic for habitual NetNews Abusers
Lines: 58


>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 identify which is which.
{}
>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.

Well, it's like this....

Twisted pair is just that. Now if you get (for example) 25 pair, each
pair is twisted around itself, then the whole group is twisted at a
slower rate. If you have 25 pair key cable, you can see this easily.
Now if you have 100 pair, each pair, each group of 25, and then all 100
are twisted at different rates. And so forth up the line, to the BIG
stuff of thousands pairs of light ;-}.

All this Chubby Checker work is to cancel out the influence of external
magnetic fields. I can remember seeing the proof in fields class, but
my memory blissfully shields {booo} me from the gruesome details.

BUT!
Old IW {interior wire} came in lots of varieties. Most of it was 'quad'
with the four conductors being Red, Green, Black & Yellow. This includes
old JTK, SK, and other stuff I cannot remember the name for. This was
NOT 2 twisted pairs. [I guess that Bell Labs never envisioned us
running Trailblazers on the Yellow & Black ;-}] IW likely has a slight
{total} twist but to tell you the truth, I never stripped back a bunch
to be sure.

More recently, I've seen installations with real 2 pair: typically
colored BL-W, and OR-W. I have NO idea what the standards are -- does
the installer now just assume we will have three lines, and thus pull 3
pair or what? [Of course, it is now YOUR wire.]

There is an old joke about the twists. In the "Good Old Daze" the cable
crew dragged the stuff down the road with a mule, then hauled it up to
each crossarm. They had to add the final {total} twist of each cable.
One of the things the foreman would do to the new guy was convince him
that the mule had been at it so long that she would stop every 1/4
mile, and roll over to add the needed twist, and roll the other way the
next time!

Now this is not a lot of help for the guy who asked the question to
begin with. I agree that he should try using the Y+B pair, being sure
that no phones are still connected to them, and see if he has a
problem. If he does, THEN worry!





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