In article , Bill Turner
writes:

On Tue, 06 Jul 2004 21:46:37 -0500, Bob Liesenfeld
wrote:

Curious. Very curious. From my experience, measuring the 'Zo of a
feedthrough cap' would be something like measuring the 'color' of a
miles/gallon rating of an automobile. Not an applicable unit of
measurement.

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Not at all. A feedthrough cap is essentially like a very short piece of
coax. Think about it. If the capacitance is small, it could well
"look" just like a short piece of 50 ohm coax. If the capacitance is
large - 1000 pf or so - that's different. It would then look like a
piece of coax with very low Zo.

It all depends.

No. 10 pFd at 1 GHz has a reactance of 15.9 Ohms. That tosses
the VSWR in the bucket if that is part of a "line section."

A "small capacitor" of 100 pFd at 100 MHz has the same reactance
of 15.9 Ohms.

Feed-throughs were designed to be SHORTS on purpose...