Keith,
In my opinion, two 40M full size 3 element Yagis would be just as effective as
three, less costly, and your 15M stack will perform better.
40M full size Yagis interact badly with 15M Yagis. Telrex dealt with this
issue 50 years ago by using shortened 40M Yagi elements. If you provide
adequate spacing (at least 1/2 wavelength on 15M) between the 40M full size
Yagi and he nearest 15M Yagis, the 15M performance should be good.
Here's a stacking arrangement you might model. You can vary the height
depending on guying constraints, etc. The critical dimension is the 25 ft
spacing between the 15M Yagis and the 40M full size Yagi.
15M Yagi 47 ft
15M Yagi 94 ft
40M Yagi 115 ft
15M Yagi 140 ft
40M Yagi 195 ft
73!
Frank
W3LPL
---- Original message ----
>Date: Fri, 11 Aug 2006 12:46:24 -0500
>From: "Keith Dutson" <kdutson@sbcglobal.net>
>Subject: [TowerTalk] Tower Planning - Stacking Antennas
>To: "TowerTalk" <towertalk@contesting.com>
>
>I have a 200 foot Rohn 55G that will be going up in the near future. On
>this tower I want to put a stack of three 3el 40M and a stack of three 7el
>15M Yagis. One of the 40M antennas will be at the top with rotator and
>mast. The other antennas will be rotated by Ringrotors.
>
>What would be the best way to stack these antennas to ensure top performance
>from the two stacks? I am thinking the 40 stack will be at 200, 134 and 68
>feet. But I am unsure about where to place the 15M antennas.
>
>Although possible, I do not think the two stacks will be used at the same
>time.
>
>Thanks in advance for your suggestions/recommendations.
>
>73, Keith NM5G
>
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