Jim,
I assume you consider a single layer coil. In that case, 23 turns over 5.3",
you get about .23" between each turn. A 10AWG wire, .101" diameter you have
about .128" air gap between each wire, provided the turns are even. The voltage
will be distributed roughly even between the turns (except at the ends) you
will have about 72 V between each turn. I think that coil will do OK at 600 W.
You can put a wire/cord between the turns when you wind the coil just to get an
even distance between the turn and, maybe needless to say, put some
paint/varnish/glue on the coil when you are finished just to make sure the wire
doesn't move when you use the antenna.
Have fun and best 73 de,
Hans - N2JFS
-----Original Message-----
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk reflector <towertalk@contesting.com>; amps <amps@contesting.com>
Sent: Thu, Jul 30, 2015 8:44 pm
Subject: [TowerTalk] Inductor Design and Voltage Breakdown
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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