> I am aware that the 5 element beam on the top will further lengthen
> the effective height from the 200 feet by (just estimating here)
> around 20-25 more feet. Will the other anten
Maybe I missed it, but I don't think anyone addressed the insulated
elements. The voltage between insulated element and the boom can be
very high when you shunt feed the tower. It can also be VERY tough on
baluns, as a matter of fact I haven't found ANY popular core-type
balun out of dozens tested that did not heat significantly with even
low levels of common-mode. That could easily be the situation with an
insulated driven element group like the KLM uses when the tower is
shunt fed.
So you have two worries...the balun heating and the parasitic
elements arcing to the boom.
I'd ground the parasitic elements to the boom through a heavy wire
air core RF choke that has a few hundred ohm reactance at the lowest
operating frequency of the yagi.
Your tower is an excellent candidate for elevated shunt feed, and may
even work quite well with a reverse feed like the N4KG feed. The
reason your tower is better is most likely the feed point could be
placed 100-150 feet above ground, and the tower BELOW that point
would look like a very high impedance at the feed point. That would
minimize unwanted and undesirable current into the tower below the
feed point, something that is especially problematic with the N4KG
feed.
The only significant problem I see is the effective height of the
radiation center would produce a pattern that is not particularly
desirable.
73, Tom W8JI
W8JI@contesting.com
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