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From: floyd@hayes.ims.alaska.edu (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Noisy phone lines
Message-ID: <1990Nov21.073343.16146@hayes.ims.alaska.edu>
Date: 21 Nov 90 07:33:43 GMT
References: <2983@hayes.uucp> <1546@westmark.WESTMARK.COM> <15994@cbmvax.commodore.com>
Organization: University of Alaska Fairbanks
Lines: 52

In article <15994@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes:
>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.
>> 
>> 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.)
>
>I'm curious about this "quad" - normal "station cable" which is what
>they use to wire up houses and the like *does* consist of twisted pairs,
>normally two of them: yellow-black and green-red.  Newer commercial
>wiring tends towards 3 or 4 pairs.
>

Despite what others are saying about "quad", you are correct, it does
have a twist.  There is a terminology problem here, but to a telco
person "quad" means two twisted pair as opposed to "spiral four" which
is also twisted, but all four together, with opposite wire forming
each pair.

There are many variations on the "twist", and in the case of drop wire
it is going to be a very long twist.  That is why people are looking
right at it and thinking it is not twisted.  Strip it back a couple
feet and they will see that in fact it is.  A shorter twist makes a
bulkier cable, so it is avoided if possible.

Even the cord to the hand set has a twist...

Floyd

PS  Alascom, Inc. is the regulated ld carrier in Alaska, just as
ATT is in the lower-48.  We are the only two regulated ld carriers,
and we do NOT compete with each other.


-- 
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.