Greetings!
You might want to do a search on SMITH CHART. There are quite a few VIs related to this, although probably none specific to cat-x. As with any transmission line, Cat-X only has a few parameters to be concerned about: loss/frequency (expressed in attenuation per 100 ft (or sometimes per 1000 ft)), and velocity of propagation, which is primarily determined by the pitch of the twist of the pair in question. Since this is thouroughly documented in the Cat-x specifications, I wonder if you can really learn anything new by trying to simulate this in Labview, other than sheer curiosity.
As far as physical interfaces for actually performing cable testing, I'm not sure if there are any off-the-shelf solutions, as this usually involves a precision
directional sampler, such as used with a network analyzer, as well as an rf detector.
Perhaps a bit more information on what you're actually trying to accomplish is in order.
Good luck!
Eric
Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705