That uses the thermal properties outside a resistor, not dielectric constant properties in a capacitor :-).
Tim N3QE ----- Original Message ----- From: ZR [mailto:z...@jeremy.mv.com] Sent: Thursday, January 30, 2014 11:28 AM To: Tom W8JI <w...@w8ji.com>; HAROLD SMITH JR <w0ri...@sbcglobal.net>; Shoppa, Tim; n...@contesting.com <n...@contesting.com>; topband@contesting.com <topband@contesting.com> Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum variables The large Bird dummy loads use oil up into the low microwave region. Carl KM1H ----- Original Message ----- From: "Tom W8JI" <w...@w8ji.com> To: "HAROLD SMITH JR" <w0ri...@sbcglobal.net>; "Shoppa, Tim" <tsho...@wmata.com>; <n...@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. > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4259 / Virus Database: 3684/7045 - Release Date: 01/30/14 > _________________ Topband Reflector Archives - http://www.contesting.com/_topband