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Re: [TowerTalk] Building a W6NL Moxon 40 Meter Beam.

To: L L bahr <>, David Gilbert <>
Subject: Re: [TowerTalk] Building a W6NL Moxon 40 Meter Beam.
From: "Richard (Rick) Karlquist" <>
Date: Sun, 03 Aug 2014 20:07:20 -0700
List-post: <">>

On 8/3/2014 2:09 PM, L L bahr wrote:
Most of the radiation comes from the current part of

 the antenna which is going to be close to the center

 point of the driven element. If you are using a U

 shaped channel 2 foot long at this area of the antenna,

 you will be pumping RF into the channel at the high

 radiation point of the antenna for 2 feet!  Looking

The center of the element that you call the high
radiation point has high current and low voltage.
The low voltage will not induce much current through
the small capacitance to the boom.  The high current
does not magnetically couple to the channel because
the channel is an open secondary of an RF transformer.
Suppose you deliberately tried the shield the center
of a dipole by putting a metal tube around it.  It
turns out that current will flow on the outside of
the pipe to replace the shielded current flowing
on the dipole inside the pipe.  Thus a short pipe
has little effect.

Rick N6RK

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