[Antennas] Capacitor Recommendation Needed

[Dennis Ashworth]

I need to insert a 1000pf of capacitance in series with my 80M vertical to 
move the resonant frequency up to the phone band. I have been using a 
vacuum variable, but would like to use it in another project - and change 
to a fixed capacitor. The logical choice would be a fixed 1000 pf vacuum 
capacitor. Failing to locate a vacuum cap, what low loss dielectric 
materials should I be considering given the frequency, voltage and current 
involved. The driving impedance is 40 ohms and I run the legal limit. 
Therefore, currents will be in the 6-8A range ... voltages probably less 
than 500 V.

Thoughts on dielectric materials and sources would be most appreciated.

Dennis, K7FL