[Amps] PTFE dielectricum variable cap

[TexasRF at aol.com]

You are right Dave, the dielectric constant is about 2.3. But, you can use  
much closer plate to plate spacing and that will increase the total C many  
times.
 
73,
Gerald K5GW
 
In a message dated 3/15/2010 5:41:47 P.M. Central Daylight Time,  
david.kirkby at onetel.net writes:

pc5m,  Carel wrote:
> Hi, I would like to get the opinion of this group on  constructing a 
homemade
> variable 500 pF/1nF capacitor for my new  160mtrs amp. To get sizes down 
I am
> considering using 1mm (40 mill)  thick teflon sheet material as dielectric
> (10 times or so capacitance  increase when comparing with air 
construction).
> So a sandwich of  several stator-PTFE-rotor-PTFE-stator-etc, etc. 
Capacitor
> stress will  be around 5KV and 20 Amps of RF current. 


I'd double-check the  relative permittivity of PTFE - I don't think it is 
as high 
as 10.  I don't say this reference can be trusted,  but

http://www.microwaves101.com/encyclopedia/permittivity.cfm

says  it's 2.2. It is certainly closer to 2 than 10 - that I am sure  of.

Dave
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