Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
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 bi...@waveform.net To: Tom W8JI w...@w8ji.com Cc: HAROLD SMITH JR w0ri...@sbcglobal.net; Shoppa, Tim tsho...@wmata.com; n...@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 w...@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 - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4259 / Virus Database: 3684/7051 - Release Date: 02/01/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
Dissipation factors for particular oils are found here: http://www.icrepq.com/icrepq'12/538-toudja.pdf I cannot comment on the accuracy of the data. Terry K4RX -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of 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. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
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 w...@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 bi...@waveform.net To: Tom W8JI w...@w8ji.com Cc: HAROLD SMITH JR w0ri...@sbcglobal.net; Shoppa, Tim tsho...@wmata.com; n...@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 w...@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 - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4259 / Virus Database: 3684/7051 - Release Date: 02/01/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
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
Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
Very true but the RF is still in the oil dielectric from the coax connector to the hot end of the resistor. Carl KM1H - Original Message - From: Shoppa, Tim tsho...@wmata.com To: z...@jeremy.mv.com; w...@w8ji.com; w0ri...@sbcglobal.net; n...@contesting.com; topband@contesting.com Sent: Thursday, January 30, 2014 11:32 AM Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum variables 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 - 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
Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
Very true but the RF is still in the oil dielectric from the coax connector to the hot end of the resistor. Not the same at all. Loss tangent is meaningless in the dummy load application because impedance is low (weak electric field). There is very little displacement current compared to current into the resistor. Loss tangent means everything in a capacitor in a coupling or tuning system, because displacement current is as high as or higher than the terminal current. _ Topband Reflector Archives - http://www.contesting.com/_topband
