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