Bill-
I've had several flavors of 'XAs and not seen this problem before. As you said
36XAs, I assume we can rule out the possibility of having the wrong thickness
tubing on the 15m caps, as has been documented many times before.
The fact that 10 is 'sort of' OK implies that the innermost trap is working
properly, isolating each element from the end sections. 'sort of' is a bit
worrisome, in that it probably only takes one mistuned/malfunctioning section
to get from 'right on' to 'sort of OK'. If there's a problem with just one
element, it would be most noticeable if the bad one was in the log cell.
The problem, in my mind, has to lie in one of three areas:
1. materials
2.workmanship
3.environment/test setup
1. Materials. If this is a brand new antenna, this would be unlikely but
possible. Check to make sure all tubing lengths/diameters are correct, and that
insuators insulate and conductors conduct. Aside from the balun, that's all
there is in an antenna! I think the matching rods typically come too long, but
that's OK.
2. Workmanship. This is the most likely area of problem. I'd strongly suggest
you get another set of eyeballs to go over all the measurements. You'd be
amazed at the number of times I can check things and consistently get the wrong
answer! Someone else (even a non-ham) may be able to recognize something wrong.
My XYL has this annoying habit of looking over my shoulder and saying 'why is
that thing over there all burned and crispy"? (Of course, she's always right)!
IIRC the spacing between capacitor sections (between plastic end caps) is
critical, should be 1/4 to 1/2 inch I think.Use an ohmeter to check for
conductivity through all joints.
3. Environment/Test Setup. If you have three antennas, how's the third one work
in the same setup? How is the feedline? Any stack matching boxes in line? Can
you use an antenna analyzer right at the feedpoint? FWIW, I've tested XA's 6
feet off the ground, and they're not as far off as what you describe. Could
there be an interaction with the lower antenna? What if you rotate one WRT the
other? Open/short the feedpoint on the non-driven one. How's the lower one look
with the upper one in place?
Good luck - 'Long Live the KT-XA's true Killer Tribanders'
-Tony, K1KP
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