It might be worthwhile to model part of the geometry (the smallest
triangle or square in the structure formed by the legs and braces of the
tower) and then move it around in Z (up and down vertically) and X
(along the boom axis) to see how much it distorts the pattern and how
much current get induced in that basic geometric element. If that in and
of itself creates a lot of distortion, then you may be in for a
difficult time. I suspect, however, it will just be a minor blip. If the
latter is true, then I would scale up the size of that basic element to
see how big it has to be before it creates any significant distortion in
the yagi pattern. That may provide a sense of how much margin you have.
Thirty inches is not even the length of a 2 meter Yagi element, so I
suspect it is going to take a much larger cross section to cause trouble.
You could start there and work your way up to a more detailed model of
the tower.
73, Mike W4EF............
On 4/26/2019 11:17 AM, Jim Brown wrote:
On 4/26/2019 10:45 AM, Gedas wrote:
One thing I have not seen mentioned (maybe I missed it) is the fact
that a whole lot of time & effort is going to go into generating a
super accurate model for a complex tower and antenna system but then,
what of the grounding of the tower itself at the base?
If I understand the original question, it's about mounting a
horizontally polarized HF Yagi on the tower at a height where the
tower is about 30-in square or triangular, not about loading the tower
itself. In this problem, whether the tower is grounded is immaterial.
What matters is that there are conductors of significant size and
cross section of the tower between two elements of the Yagi. The issue
I see is how the tower interacts with the Yagi -- that is, how does it
affect the interaction between the elements of the Yagi to it's
directional pattern and SWR.
I have no experience with this, but lots of contesters have HF Yagis
mounted like this on various sizes of triangular towers.
73, Jim K9YC
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