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Re: Topband: Shunt Feed - Insulated Elements on Yagi

To: <>, "Ralph Parker" <>
Subject: Re: Topband: Shunt Feed - Insulated Elements on Yagi
From: "Tom W8JI" <>
Reply-to: Tom W8JI <>
Date: Sat, 20 Dec 2014 10:10:04 -0500
List-post: <">>
You can model this two ways:

1.) As a very high impedance load between the elements and the boom and look at the load data to see voltage between the boom and elements

2.) With a source between the element and boom, and set the source to zero current. Then look at source data and see what the voltage is to have zero current. This will tell you the peak voltage.

Arcing and damage absolutely can be a problem, and not just on 160. I know a few people who have an insulated element antenna stacked above or below a differently rotating antenna, and when the second antenna's elements are near parallel to the boom the boom is excited so much it arcs to the elements. This is an issue when a boom length near 1/2 wave on the second band is excited by the second band.

It is also an issue on 160. The less "other large stuff" at the top and the more power, the more of an issue it becomes.

----- Original Message ----- From: "Ralph Parker" <>
To: <>
Sent: Thursday, December 18, 2014 7:59 PM
Subject: Topband: Shunt Feed - Insulated Elements on Yagi

Good question, Stan. I've wondered the same thing.

I have a 64' self-standing tower with a 3 el Steppir on it (insulated
elements) and a 40m linear loaded dipole (also insulated) on top of that.
I've worried that any high voltage on the ends of the boom might be harmful
to the drive motors in the dir/ref boxes.
So I've chickened out and avoided loading the tower on 160.


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