Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!grr
From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: comp.dcom.modems
Subject: Re: Noisy phone lines
Message-ID: <15994@cbmvax.commodore.com>
Date: 21 Nov 90 00:39:33 GMT
References: <1990Nov15.193826.3875@beach.csulb.edu> <2983@hayes.uucp> <1546@westmark.WESTMARK.COM>
Reply-To: grr@cbmvax.commodore.com (George Robbins)
Organization: Commodore, West Chester, PA
Lines: 34

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.

In any case it would take a considerable amount of crosstalk to cause
problems either way.  The real concern is when there exits only one
two-wire cicuit and the phone company uses special "carrier" equipment
to multiplex a second circuit rather than route additional wires...

-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr@cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)