Phil said:
I'd measure the capacitance on the scope end, add 10 pF for the scope,
and then divide by 9 to match the voltage divider. That of course
neglects other capacitance in the circuit, but for a trimmer it ought to
be reasonably close.
Yes, I'll probe it out if there is no schematic. But these things are
way more complicated. IIRC there were several other trim caps and three
potmeters or so in there. Plus some fixed value SMT components. The
gold-plated BNC as well as the tip cable are clicked into slip ring
holders. Quite impressive, actually.
At least I was able to finish the measurement by wedging a piece of
toothpick in there. Not so with the baseband analyzer. It had been
literally destroyed in shipping. Wanted to measure phase noise on VCSELs
but I guess that has to wait now :-(