On Wed, 23 Dec 2009 14:00:39 -0500, Rex Lint wrote:
> Wouldn't a hefty variable work just as well? $15 compared
>to $80 or so?
You're correct -- when you're feeding at a low impedance point
(near a quarter wave from the open end), it's not voltage, it's
CURRENT and dissipation (LOSS). A local surplus house here in
Silicon Valley has a lot of HV rated capacitors in bins. I bought
a bunch of them to use for things like this, but I didn't have
easy access to data sheets to learn about their equivalent series
resistance. My solution was simple -- I tried various parts at
the feed point of my 160M vertical that needed series capacitance
to match it, keyed the legal limit amp for a while, and then went
outside to see if they were cool, warm, hot, or smoking.
All the capacitors I tested were rated for 3kV or more, but some
smoked and some ran quite cool
73,
Jim K9YC
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