Well here's what I did: I treated it like a peice of coax. I made a
fixture to hold the "feedthru" with semi-rigid coax on one side and a
50 ohm chip resistor on the other. I dropped in a short peice of coax
and cal'ed to that. Then checked VSWR, was about 1.00something. Then I
took out the coax, dropped in a few feedthrus and got VSWRs about 1.04
- 1.06, which works out to about 53 - 55 ohms or so.
How's that sound?