[TowerTalk] Top Loading Shunt Fed Tower

[Michael Tope]

At our club station, we are stacking a KT-34XA 10' above a KLM 40M4
(40 meter 4 el yagi). The antennas will go on a 60' tower which is sitting
on top of a 40 foot tall building. There is another sub-building/doghouse
on top the building whose roof is about 45 feet below the top of the tower.
This turns out to be a convenient point to shunt-feed the tower (the rotator
cables and RF feedlines come off the tower at this point). Since I am
interested in 160 meters, I am shorting the parasitic elements on the
KLM antennas to their respective booms in order maximize their
contribution to top loading.

Yesterday while I was intalling the shorting straps on the KT-34XA, my
friend suggested that I was wasting my time since the larger 40M4
would dominate the top loading. Intuitively, this seems reasonable, but
after having thought about it some more I am not sure. Would the
fact that the KT-34XA is 10' higher than the 40M4 compensate for the
fact that the XA is smaller, or will the larger size of the 40M4 swamp
out the XA? Also, can anyone hazard a guess at what the electrical
height of the 45' tower will be when the 40M4 and the KT-34XA are
stacked on top?

Thanks,

Mike, W4EF


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