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Re: Topband: Submerging variable caps in oil as substituteforvacuum vari

To: "Tom W8JI" <w8ji@w8ji.com>, "HAROLD SMITH JR" <w0rihps@sbcglobal.net>, "Shoppa, Tim" <tshoppa@wmata.com>, <n4zr@contesting.com>, <topband@contesting.com>
Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
From: "ZR" <zr@jeremy.mv.com>
Date: Thu, 30 Jan 2014 11:28:43 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
The large Bird dummy loads use oil up into the low microwave region.

Carl
KM1H


----- Original Message ----- From: "Tom W8JI" <w8ji@w8ji.com> To: "HAROLD SMITH JR" <w0rihps@sbcglobal.net>; "Shoppa, Tim" <tshoppa@wmata.com>; <n4zr@contesting.com>; <topband@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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