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Re: [TowerTalk] Vacuum variable / inductor ratings for shunt fed tower

To: "K4SAV" <>
Subject: Re: [TowerTalk] Vacuum variable / inductor ratings for shunt fed tower
From: "Rick Karlquist" <>
Date: Thu, 11 Jun 2009 13:28:24 -0700 (PDT)
List-post: <">>
K4SAV wrote:
> I wouldn't recommend using the SteppIR elements as a capacity hat.  The
> elements are insulated from the boom and most of them won't add a lot a
> capacity.  The driven element has a 2 to 1 balun.  It also does a choke
> function. The primary to secondary capacitance of that balun will
> conduct some current and cause some dissipation.  The balun is unlikely
> to have a high impedance on 160 meters.  It will also have a lot a
> voltage across it.  I have not heard of anyone reporting a destroyed
> balun, and I have heard of some people using the SteppIR elements for

I don't agree with "a 2 to 1 balun ... also does a choke function".
First of all, the impedance ratio is 9 to 4, and the turns ratio is
3 to 2.  Second, all "current baluns" or "common mode chokes" are 1:1.
I have never seen one that is not.  I spent a lot of time analyzing the
balun in my MonstIR and characterizing it on a network analyzer.
IIRC, the balun is of the "voltage balun" type with a center tap connected
at least to the outer conductor of the coax, if not the boom.  If you
simply connect the outer conductor to the boom, near the balun, you should
be OK.  You could probably get away with bonding the coax outer conductor
to the tower near ground level in many cases.  You do need to do something
to keep RF off the control cable of the SteppIR, but this problem
exists whether or not you extend the elements to use as a capacitive
hat.  If this is wrong, somebody correct me.

Rick N6RK


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