Topband: Submerging variable caps in oil as substituteforvacuum variables

[Bill Wichers]

SF6 is sulphur hexaflouride. It's a dielectric gas, not an oil. 

For everyone thinking about oil there is also silicone oil available. I have no idea if its better or worse for rf though -- like Tom said, dielectric oils aren't usually specified for rf performance. 

-Bill

Sent from my iPhone

On Feb 2, 2014, at 8:16 AM, "Tom W8JI" <w8ji at w8ji.com> wrote:

> 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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