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[TowerTalk] Tower Height Question - Dual Yagi's

Subject: [TowerTalk] Tower Height Question - Dual Yagi's
From: Greg Beam <>
Date: Wed, 17 Jun 2009 04:04:04 -0700 (PDT)
List-post: <">>
Hi All, 

Having been bitten by the DX and Contest bug, I was having a chat with a 
friend Larry, K7MI, and he really has my mind moving (spinning more like) about 
antenna / tower configurations which has prompted me to query about a few 

I'm in the design ( Thinking ) phase of building my first tower ( lots of 
things to consider for sure ) and I'm looking to find the optimum height and / 
or configuration for a pair of Yagi's as well as to maximize the overall use of 
the tower itself.

Hardware Under Consideration (but not limited too):
40M - Force-12  - 240N 2L (~10.7sqft wind load)
10-15-20 - Force-12 C-31XR (~10.7sqft wind load)
Tower Type: Rhon 45G
Rotator: PST2051 / PST61 or Equivalent Load Specs
Primary Interest: DX & Contesting

All the engineering precautions will be adhered to for guys and wind load 
safety, which will include dual Phillystan 6700 guys (maybe 11200) at each 
level & guy point.

I'm considering a TH7 or TH11 (WARC band Bonus) instead of the C-31XR (purely 
from a cost perspective), which has a similar wind load figure but I'm not 
thrilled about the idea of having traps for a long term installation.

I would like to have an 80/160 Vertical / Inv-L configuration using the tower 
as the radiating element, but do not want to compromise the optimum heights for 
the Tri-Bander & 40m 2L Yagi. Obviously this would be either an end-fed 80m 1/2 
wave situation or a full 1/4 wave 80m + 160M Inv-L switching configuration.

>From my understanding, ~70' is the first optimum point for a 40M Yagi (please 
>advise if this is not the case) so a tower height of 60' + 10' above the 
>Tri-Bander would would do nicely, but would there be any advantage / 
>disadvantage ( apart from cost ) in going the additional 30/40ft to say 100' 
>to 110' or there abouts, which would get me close to what I need for a full 
>size 1/4 wave 160 vertical and double as a 1/2 wave End-Fed for 80m? 
>Alternatively, could I possibly go lower on the initial tower height, using 
>the Yagi's as CAP hats to bring the overall electrical length up for 80m/160m 
>without compromise to the Yagi's performance? 

Any Additional Options / Thoughts / Ideas would be greatly appreciated.

Best Regards,

Greg, KE1HA
Helena, Montana



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