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@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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