Topband: Submerging variable caps in oil as substituteforvacuum variables

[ZR]

The large Bird dummy loads use oil up into the low microwave region.

Carl
KM1H


----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: "HAROLD SMITH JR" <w0rihps at sbcglobal.net>; "Shoppa, Tim" 
<tshoppa at wmata.com>; <n4zr at contesting.com>; <topband at contesting.com>
Sent: Thursday, January 30, 2014 5:32 AM
Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum 
variables


> 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.
>
>
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