I'm designing a special 80M vertical for CQP (California QSO Party)
county expeditions that can be self supporting for places where there
are no trees. For it, I need a 20 uH loading coil. NEC tells me that
running 600W, it will see about 1650V and about 3.5A. I'm concerned
about voltage breakdown, so I've scoured the ARRL Handbook and the
internet, and can't find any guidance. W8JI's webpage discusses the
issues, but has no specific advice except to say that it can be a problem.
N6BV pointed me to a couple of ancient DOS programs that are good at
predicting Q, inductance, stray C, and dissipation, but don't address
voltage breakdown. And I had to find an old computer to run them on.
Surely there must be good stuff around.
I'm tentatively thinking about 23 turns of #10 bare or enameled copper,
3-in diameter, about 5.3-in long. That works out to about 4.5 turns/in.
Suggestions?
73, Jim K9YC
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