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Re: [TowerTalk] Fan dipole Re: Looking for a HP 80/40 Duplexer

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Fan dipole Re: Looking for a HP 80/40 Duplexer
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 18 Nov 2025 22:30:51 -0800
List-post: <mailto:towertalk@contesting.com>
On 11/18/2025 7:50 PM, john@kk9a.com wrote:
When I saw fan dipole listed as the 40/80 antenna I was thinking of a
homebrew dipole with separate wire elements attached to a common center
insulator (and maybe choke).

Since we can't do attachments on this reflector, I'm posting a link to a pdf of VERY old slides for a "practical antennas" talk I did for a local club soon after moving to W6. Page 11 shows the loading coil for an 80/40 loaded dipole, pages 15 & 16 show current distribution. Pages 26 and 27 show the first fans I built after moving here. This was an antenna sold in the back of QST by a guy in PA, that I bought when I was getting back on the air in Chicago in 2003, and didn't have the stash of stuff to build something. The loaded design just fit between the two points where I could get a friend to rig it (the roof of the house was WAY too steep for me).

http://k9yc.com/LimitedSpaceAntennasPPT.pdf

BTW -- I've changed my thinking about the effectiveness of vertical dipoles after the extensive modeling study I did about ten years ago, showing the dependence of verticals on soil quality. Ground quality at my QTH is really poor.

73, Jim K9YC

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