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Re: [TowerTalk] References for using a grounded tower as a vertical radi

To: towertalk@contesting.com
Subject: Re: [TowerTalk] References for using a grounded tower as a vertical radiator
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 23 Jun 2023 20:04:50 -0700
List-post: <mailto:towertalk@contesting.com>
On 6/23/2023 11:51 AM, john@kk9a.com wrote:
Other nearby towers or vertical metal structures can severely distort the
radiation pattern.

Yes. Also "somewhat vertical" wires like the feedlines to wire antennas like horizontal dipoles. These things can be modeled if we know dimensions, including spatial details. I spent much of a summer about ten years ago working out the interactions between a 120 ft tower with antennas on top with my 100 ft Tee vertical for 160M; and between the Tee and a pair of sloping wire verticals hanging from the tower that I feed one at a time against radials.

The tower acts as a reflector for the Tee, yielding a few dB gain to VK/ZL (also a corresponding null to Seattle), and as a reflector for the sloping wires yielding a few dB in the direction of the slope; the Tee acts as a reflector, kicking both patterns north by about 30 degrees, yielding a few dB into JA or EU, depending on which I'm feeding. To make all this work, I had apply a short at the base of the antennas that acted as reflectors, which I did with a combination of feedline length ad stubs.

73, Jim K9YC


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