[Lowfer] Musical capacitors and dissipation loss

[Lisa Cianciolo]

Hello Again,

Anyone ever hear of a trombone capacitor?  Basically 2 pieces of copper tubing that are slipped inside each other, isolated with a dielectric such as teflon.

Why should you care, well maybe you shouldn't but in an effort to rid myself of mechnical connections, I anm looking at this method of tuning my MEDFER loop.

With 2 pieces of brass tubing about .5" dia and 10" long and a slip fit, I was able to make a very stable 230 Pf capacitor that was very stable.  Stable, as in all the compression types I made changed capacitance over time (minutes) as the dielectric changed shaped or flattened out. The only teflon I used was at the very outer ends of t he tuning so really it was used more as a bushing then a dielectric.90% of the tubing was air space.

Has anyone ever tried these before?  I only need 520 Pf or for the MEDFER loop.  So this  method may and work tuning was very smooth.

The other question I have is my LCR meter tests at 1 Khz, not really adequate for measuring dissapation factor at 1700Khz.

Does anyone know of a test that I could perform, even a relative test, to compare the air against say a silver mica?

Any help would be appreciated.  Thank you

PaulC

W1VLF




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