Two of the three KT36XA's I have in my stack have mild to severe SWR
problems. I've swapped out the balun with a new one from M2 and also
swapped with the balun from the one good XA. I've ruled out a balun
problem.
The lowest antenna was OK on 15M, but poor on the low ends of 10 and 20
meters. I'm on CW about 99 percent of the time, so problems on the low
end can't be ignored. Since the low antenna was easiest to take down,
I'm working on it first.
I've measured the resonance of all of the individual elements, one by
one, and have that information available in a spreadsheet. Readings are
in the ballpark with N2IC, W4EF, and K1KP values. After taking the
antenna down, checking all measurements, cleaning all joints, etc. I
have the following SWR curves with the antenna hanging in the clear from
a rope at 25 feet. These are very similar to what I measured with the
antenna still on the tower, before taking it down.
14.0 2.8
14.1 1.7
14.2 1.6
14.2 1.6
21.0 2.2
21.1 2.2
21.2 2.2
21.3 2.2
21.4 1.7
28.0 3.0
28.2 2.2
28.4 1.9
28.6 2.0
28.9 1.6
For those of you that have dealt with these antennas, how do you go
about adjusting the elements to get the SWR down? I assume that if I
move the inner 10M shorting strap towards the boom, this will lower the
10M resonance and vice versa. If I move the outer shorting strap away
from the boom, this will lower the 15M resonance and vice versa. I
would expect changes in the 10M setting to affect 15M and 20M, and
changes in 15M to affect 20M. Extending the tip length should lower the
20M resonance.
I've read that the rear driven affects mostly the lower end of the SWR
curve, while the front driven affects mostly the higher end of the SWR
curve. Based on this, should I try lengthening the 10M Rear Driven for
starters?
73
Randy K0EU
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