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.
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