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