First of all, thanks a lot for all contributions so far ! Seems to be a fun
project to take on : - )
One thing I did in the meantime was to calculate/check the field strength
in the airgaps which will occur between stator-ptfe sheet-rotor combination
(5KV, 1mm[40mil] PTFE, twice 0.1 mm[4mil] air gap). If I did the math
correct it turns out that the E-field will be around 10KV/mm ! And as above
3KV/mm air will breakdown this is not good...eating up the PTFE/corona/etc
Funny thing is that basically how small you make this inevitable airgap
(e.g. 0.001 mm / 0.04 mil ) still the E-field will remain too high. Seems
to be logically as you have basically 3 capacitors in serie: 2 big "air"
one's and one relative small PTFE one with the resulting capacitance.
Decreasing the air gap -> air capacitor linear increases -> RF voltage
across it will linear decrease-> resulting RF voltage divided by distance
stays the same..
As I don't want to mess with oil and PTFE plating is too expensive (not in
the oil business as well.) it seems this is a real problem (THE problem with
this kind of contraptions?).
To be continued.
Thanks again, Carel.
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.
Did google a bit,but no hits.should this be attainable ? I think losses of
PTFE are well enough at 2 MHz to cause any heating or change in Eps
R/capacitance and 40 mill will provide enough rigidness and stability ?
Thanks, Carel
p.s. Yes, of course I do know that vacuum capacitors do exists ...
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