[TowerTalk] Fwd: Inductor Design and Voltage Breakdown

[Hans Hammarquist]

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 at audiosystemsgroup.com>
To: towertalk reflector <towertalk at contesting.com>; amps <amps at 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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