Topband: Submerging variable caps in oil as substituteforvacuum variables

[ZR]

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" <tshoppa at wmata.com>
To: <zr at jeremy.mv.com>; <w8ji at w8ji.com>; <w0rihps at sbcglobal.net>; 
<n4zr at contesting.com>; <topband at 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:zr at jeremy.mv.com]
> Sent: Thursday, January 30, 2014 11:28 AM
> To: Tom W8JI <w8ji at w8ji.com>; HAROLD SMITH JR <w0rihps at sbcglobal.net>; 
> Shoppa, Tim; n4zr at contesting.com <n4zr at contesting.com>; 
> topband at contesting.com <topband at 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" <w8ji at w8ji.com>
> To: "HAROLD SMITH JR" <w0rihps at sbcglobal.net>; "Shoppa, Tim"
> <tshoppa at wmata.com>; <n4zr at contesting.com>; <topband at 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.
>>
>>
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