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Re: [TowerTalk] 80M Ideas

To: towertalk@contesting.com
Subject: Re: [TowerTalk] 80M Ideas
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 28 Dec 2012 01:30:59 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 12/27/2012 7:50 AM, Jack White wrote:
I have a painted 3 section 60ft Versatower (suspect v. poor electrical 
connection between sections) with an Optibeam OB1-4030, Optibeam OB9-5 and 5L 
6M Yagi all mounted on a 15ft stub mast

Several thoughts.

1) You may think that the connections are crummy, but a smart EE friend who works with towers a lot has observed that with all the weight that's on it, and the considerable cross sectional area in contact at the tower junctions, most towers are likely to have connections good enough to load. I'd say it's worth a try.

2) That tower WILL interact with any vertical antenna that you put anywhere near it, and "near it" is within more than 100 ft on 80M. My 120 ft tower interacts enough with my 160M vertical that's about 210 ft from it to give me 3dB of useful directivity going south, and a 3 dB null going north. If I model my 45 ft tower with a couple of monoband Yagis on a 16 ft mast, it puts a 2dB bump in the 160M vertical.

3) If I were you, I would study the ARRL Handbook, the ON4UN book, and the ARRL Antenna Book on the topic of loading towers, and I would also study N6LF's excellent website, and I would use what I learned to either load that tower or use it as a passive reflector for another vertical. Rudy has a great paper on tower interaction that will surprise you. It sure surprised me, and NEC confirmed what he was observing.

4) Consider the possibility of hanging a sloping wire off the tower, fed from the botom of the wire, insulated from the tower. Depending on the tower height, it may work as a passive reflector, and as you describe it, I suspect it will. I'm doing exactly that on 160M, and it works well. You will need radials on both the tower and the sloping wire.

73, Jim K9YC

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