[TowerTalk] Problems with the KT36XA

[Tony Brock-Fisher]

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