Topband: Submerging variable caps in oil as substitute forvacuum variables

[Tom W8JI]

Still I am intrigued by the thought of a remote tuning capacitor via 
hydraulic tubing :-). The capacitor plates could be as simple as two 
concentric cylinder conductors with appropriate spacers. I betcha crud 
collecting on the top of the oil would set voltage limit.>>>

I would be as concerned, or more concerned, with the dissipation factor of 
the oil at short wave frequencies.

The thing that worries me is I cannot recall every seeing a single good 
high-Q oil-dielectric capacitor above power line and audio frequencies. As a 
matter of fact, many years ago I tried to use a surplus 20-40kV oil 
capacitor from Fair Radio as a plate blocking capacitor, and it overheated 
so badly it exploded.

I looked for HF data on mineral oil as a dielectric and couldn't find 
anything. That would be my main concern. I guess I could stick mineral oil 
between the plates of a capacitor and see what happens to Q.