"Chris" wrote in message
...
Hi,

I'm currently having to build some high-voltage capacitors for an auto-ATU
that I'm building. The capacitors are made from interleaving brass shim
with some kind of dielectric. It was suggested that the dielectric was
made
from a triple layer of polyethylene sheet (ie freezer bag) stuck together
with DC4 grease to exclude any air. However, this seems a messy approach
and some engineer friends suggested that instead I use overhead projector
transparency. I found that a double layer of this transparency worked to
give me reasonable capacitor values with a reasonable number of plates per
capacitor.

I would be a little concerned about the loss factor of the transparency
material. The polyethylene originally suggested is an excellent dielectric-
the transparency material may yield reasonable capacitor values, but if the
loss factor is high, wach them smoke.
As suggested, teflon is also excellent.
For the lower values a good qulaity 50 Ohm coax will yield about 29pF/foot.

Dale W4OP