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From: esmith@apple.com (Eric Smith)
Newsgroups: comp.dcom.telecom
Subject: Re: Crosstalk on Two Lines on One Four-Wire Cable
Message-ID: <12018@accuvax.nwu.edu>
Date: 10 Sep 90 00:27:20 GMT
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In article <11864@accuvax.nwu.edu> tcora@pica.army.mil (Tom
Coradeschi) writes:

>   The phone on my desk and the PhoneNet drop into my office use two pair
>   from the same line. I've honestly never noticed ANY noise in the phone
>   line - and I spend a LOT of time on the phone - and never noticed any
>   AppleTalk problems due to the phone being in use. This goes for both
>   voice transmissions, as well as data, i.e. modem (remember, I don't get
>   two lines:-{).

That's because LocalTalk (the physical layer, AppleTalk is the
protocol stack) uses much higher (non-audible) frequencies.  Voice or
modem one the main pair and LocalTalk on the secondary pair may have
some coupling, but will not interfere with each other under normal
circumstances.

I have a Telebit Trailblazer+ and my voice line on two pairs on one
cable at home, and the coupling is very obvious to me, but people I
talk to claim not to hear it.  I plan to rewire using real twisted
pair in the near future.


Eric L. Smith      Opinions expressed herein do not necessarily reflect those
esmith@apple.com   of my employer, friends, family, computer, or even me!  :-)