[TowerTalk] Tower Height Question - Dual Yagi's

[Greg Beam]

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 things.

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