Path: utzoo!utgpu!watserv1!watmath!att!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!apple!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: <1990Nov21.140128.28529@hayes.ims.alaska.edu> Date: 21 Nov 90 14:01:28 GMT References: <1546@westmark.WESTMARK.COM> <1990Nov20.131818.28875@hayes.ims.alaska.edu> Organization: University of Alaska Fairbanks Lines: 46 In article urlichs@smurf.sub.org (Matthias Urlichs) writes: >In comp.dcom.modems, article <1990Nov20.131818.28875@hayes.ims.alaska.edu>, > floyd@hayes.ims.alaska.edu (Floyd Davidson) writes: >< In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes: >< > >< >[...] 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. >< >< Each pair is twisted. Other than that the only placement or >< arrangement done is to make it easy to identifiy which is which. >< >One other "arrangement" is usually done: each twisted pair has a different >number of twists per length, to avoid two pairs being "twisted in sync" which >may still allow crosstalk. >(Or at least the cables I have are manufactured this way.) > On larger cables (not "quad") every pair in each bundle has a different length to the twist. And they are laid into the bundle in such a way that pairs with the closest twist are less likely to be physically next to each other. I am not positive that quad is not done the same way, but I've never seen anything saying it was (or wasn't for that matter). My point was that "quad" is twisted pair cable. With that said I'll through another one in on the subject of crosstalk on modem lines. Consider the fact that every extention line run off in a different direction from your demark point is *unterminated* when the phone or modem at the end of it is on-hook. If these stub lines are very short or very long they don't make any difference, but there is some point in between (I'd have to guess at what a significant length would be) that unterminated line is going to cause all kinds of problems. Comments??? 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.