Topband: Submerging variable caps in oil as substituteforvacuum variables

[Tom W8JI]

The major issue with dielectrics is dissipation factor at 2 MHz, which 
affects losses and Q. Dissipation factor is not published all the time. I 
can't find dissipation factor for mineral oil.



----- Original Message ----- 
From: "Bill Wichers" <billw at waveform.net>
To: "Tom W8JI" <w8ji at w8ji.com>
Cc: "HAROLD SMITH JR" <w0rihps at sbcglobal.net>; "Shoppa, Tim" 
<tshoppa at wmata.com>; <n4zr at contesting.com>; <topband at contesting.com>
Sent: Saturday, February 01, 2014 4:05 PM
Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum 
variables


I was reading this thread and all the concerns about oil in the capacitor. 
Has anyone ever thought about trying SF6 as a dielectric? It's commonly used 
in high voltage (hundreds of kilovolts) switchgear by utilities.

Just a thought, more curiosity than anything else.

-Bill

Sent from my iPhon

On Jan 30, 2014, at 5:32 AM, "Tom W8JI" <w8ji at w8ji.com> wrote:

> 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.
>
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband


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