You probably have a current fed vertical so you don't have to worry
very much about the voltage on the cap. Any air variable with around
1/4 inch spacing will be fine. It should not be hard to find
something with the value you need--the tune cap in any ham RF amp will
probably be okay as an example of what to look for. Put it in a wx
shielded enclosure. Another thing to look for that is ridiculous
overkill but cheap are fixed vacuum caps--most hams have no idea what
to do with them so they are inexpensive on eBay and you can put a
short bread slicer paralleled with one to vary it. look for 200
pF--they will handle all the current you want to put out for ham power
levels. Doorknobs are effective but expensive. Old micas can be
leaky. I'd just use an air variable and be done.
73
Rob
K5UJ
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|