Twisted Pair

On Sun, 08 Dec 2013 10:41:37 -0700, Jim Thompson Gave us:

using cat 5e specs and hardware and calling it cat 6 would yield lossy operation at the upper end.

There's enormous variation in twisted pairs, even among "standard" things like compliant CAT5 and CAT6 cables.

The Spice lossy delay line implements The Telegrapher's Equation, but ignores skin loss variation with frequency. The best thing to usually do is get a chunk of the actual cable of the expected length and note its step response on a scope, then fiddle the Spice lossy line parameters to match. An extra RC or two sometimes helps fine-tune the model to reality.

Multi-pair cables, like CAT5/6, can be expected to have various amounts of crosstalk and pair delay skews, too.

Simple RC equalization helps, if the cables are repeatable.

Thanks! Good collection of data there in your examples!

I do remember doing compensation BC (before CAD) using a pre-emphasis leading-edge pulse... on a thousand foot chunk ;-)

I'll look at how PSpice does their lossy T-line, and maybe I can adapt. I did some lecturing on skin-effect modeling for Intel eons ago... I'll review my notes. ...Jim Thompson

On Sun, 08 Dec 2013 11:55:30 -0700, Jim Thompson Gave us:

This has to be a first.

Or at least the first in a long time.

Could this mean that the group might actually get back on a/the scientific/proper track again?

Looks to me like you pointed him onto the right path, and also that he may actually know more about what effects are in play than you do, just has to dig up some recollection between glasses of wine or some such.

The book, , addressed SDL over standard ol' twisted telco lines. Is that of interest?

The results are a mix of formulas and empirical information supposedly better than 1% between DC and 10MHz for either 24 or 26 Awg twisted pair.

be careuful, my edition has 'errors' in them and you need to look at them before using them.

"ADSL/VDSL Principles" by Dennis J. Rauschmayer, 1999 Macmillan Technical Publishing pp 28-42

from URL:

ADSL/VDSL principles a practical and precise study of asymmetric digital subscriber lines and very high speed digital subscriber lines Dennis J. Rauschmayer. Published 1999 by Macmillan Technical Publishing in Indianapolis, IN . Written in English.

Aioe won't let me put in all the lines, so I'll send directly to you a sample of the 'corrected' formulas for 26Awg wire and uncorrected 24 Awg wire.

Anybody else want them, email me, or let me send to you and you can post them.

Got them, Robert, Thanks! ...Jim Thompson

You're welcome. Were 'grunt' models what you were after? What you doing?

You're welcome, but whatcha doin' with 'em? ? ? ?

On Wed, 11 Dec 2013 07:00:24 -0700, RobertMacy Gave us:

Diddling...

A simple data link. ...Jim Thompson

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Just ran across a formula for twisted pair appearing on a single ppt slide. Formula predicts for ANY cable, requires dimensions and dielectric constants, and looks good; will send that to you, too.

Thanks! ...Jim Thompson