I still question this assertion that mica degrades at HF. According to the
best information I have ( which I will be glad to post if anyone cares) mica
has a loss factor of 2x10^-4 at frequencies up to 100MHZ. It is virtually
flat across the spectrum (the data I have does not go beyond 100MHZ.) and is
one of the lowest loss (dielectric) materials on the planet.
I build all of my own HF high-power capacitors and use mica wherever
possible, teflon and UHMW otherwise. When I measure a finished capacitor on a
vector Z-meter I typically can't even resolve any deviation from 90 degrees
in the phase angle. I admittedly haven't tried the same with any of these
ceramic-capacitors-on-steroids because I just can't stand seeing any of them
sitting inside of one of my amplifiers (at least not in a HI-Q circuit.)
However, now I am going to at least make some measurments and see if anything
shows up in the phase angle that is significant.
If you have some information that proves that there are better capacitor
dielectrics for HF than mica, teflon, or polyethylene, let's see it.
Otherwise, let's put an end to this myth that mica is an inferior capacitor
dielectric at ANY HF.
Eric von Valtier K8LV
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