I thinking of trying other capacitors, how about following combinations
mica fixed + mica variable
mica fixed + air variable

Another option is to homebrew your own capacitors. I've seen
descriptions of magloop-antenna tuning caps of a number of interesting
sorts which are fairly easy to homebrew:

- A sheet of glass as the dielectric, with metal plates (or the
surface copper of sheets of PC-board material) as the electrodes.
These can be made variable by arranging to slide one
plate-electrode over, or away from, the other.

- Fixed caps made of PC-board material (etch away a strip around the
edge of each side to prevent arcing)

- "trombone" caps made of concentric copper or brass pipe or tubing,
with Teflon or polyethylene film rolled onto the inner tubing as a
dielectric.

If you only require single-frequency operation you might be able to
build a metal-and-glass or PC-board fixed cap which has more capacity
than you need, and them trim it (literally) by removing a bit of the
metal at a time until you reduce the capacity to the value which
establishes resonance at your operating frequency.

--
Dave Platt AE6EO
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