[TowerTalk] Conversion to W6NL 40M MOXON

[W0UN -- John Brosnahan]

>
>After a quick look at the paper and the associated .gif drawing that gave 
>the tubing sizes, I couldn't help wondering about the structural soundness 
>of the intersection between the elements and the loading structures, which 
>involve two different sizes of element tubing and a third size in the 
>cross pieces.  Dave literally wrote the book on physical design of yagis, 
>but that looks like a pretty critical area.  Didn't I hear somewhere that 
>NT1Y's new 80M F12 yagi failed at similar points in the elements?

Just FYI.   NT1Y's failure was not due to any structural issues
that are relevant to the Leeson/Moxon design.  The F12 Yagi
has top guys that are center mounted so low that under some
ice conditions the tips can bend down enough to raise the pre-guy
section to have the guys end up on the wrong side of the element
and actually pull down rather than up.  Or so it appears to me
after reviewing the photos of the failures.

There are a lot of ways to make a Leeson/Moxon antenna so that
the loading is structurally stronger than the rest of the element.  One
obvious way is to mill a block of aluminum so that one side has
a groove to match the diameter of the element and the other side
has a groove at right angles that matches the diameter of the loading.

Another way is to make a clamshell similar to the Hygain element
to boom mounts.  In any case the results of the modeling are very
promising and it would be a lot of fun to play with the antenna to
see how close a real one is to the model.

--John  W0UN
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