FWIW, when I was building my first tower, 14 years ago, I was
planning to go with 70 feet. W3LPL, who is (and has been) at the top
of the class for antenna and propagation expertise, strongly urged me
to go to ~100 feet for a single-tower station, and to put the 40M
beam on top. I did it, and have been glad I did.
I use this tower to support an 80-meter wire parasitic array (not
quite a 4-square, but a lot simpler to build), and shunt feed it on
160 with good results.
The tower currently has an EF-240S (F12) on top and two C-3Es (also
F12). I deliberately chose these antennas because they are small and
light enough (~30 pounds) that I could handle them on the tower,
while the C-3E stack gives me gain approaching that of a single
bigger tribander, and angle diversity that it can't match.
73, Pete N4ZR
At 07:04 AM 6/17/2009, Greg Beam wrote:
>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.
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