TopBand: KT-34xa and top-loading a shunt-fed tower

Mon, 15 Sep 97 00:44:25

Hello all:  I'm looking for some advice and the benfit of someone's 
experiece in using the KLM KT-34xa tribander as top-loading for a shunt-fed 
tower on 160m.  

The KT-34xa, as many of you know, is a six-element yagi for 10, 15 and 20m.
The elements are approximately 25ft (7.5m) long, and the boom is 32ft (9.5m) 
long.  I will shortly install this beam atop an 84ft (25m) tower.  The
elements of the tribander are insulated from the boom.  

According to the formula provided on page II-32 of the 1988 edition of 
ON4UN's excellent book "Low Band DXing,"  the surface area of a beam atop 
a tower adds substantially to the electrical length of the tower when used 
as a shunt-fed vertical.  

If the whole surface area of the KT-34xa contributes to the top-loading of
tower, the electrical length of the system at 1.830MHz should be 
approximately 81 degrees.  If, because the elements are insulated from the
boom, they will not contribute to top-loading the tower, I have calculated
that the boom alone will make the electrical length of the system at 
1.830MHz approximately 61 degrees.

I would prefer to use a vertical 81 degrees long than one 61 degrees long.

I now have two questions, which I hope one of you better minds may answer:

1. Given that the KT-34xa's elements are insulated from the boom, will those 
   elements contribute to the top-loading of the tower?

2. If they will not contribute, would the performance of the KT-34xa degrade
   if I connect the reflector and the third director to the boom?  My idea
   is that by connecting these two elements (the ones at the extreme ends)
   to the boom, they would contribute to top-loading the system.

If anyone else has thought of this situation, or has tried connecting any 
of the parasitic elements of the KT-34xa to the boom, please share your
knowledge and experience with me.  

73,

Dave VE2ZP/VE9CB
ve2zp@bbs.ve3jf.ampr.org

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