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
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