On Tue, 22 Sep 1998 16:02:12 -0500 WE9V Chad Kurszewski
<Chad_Kurszewski@csg.mot.com> writes:
>
>Hi All,
>
>I'm about to put up the first KT-34XA this weekend. Upon checking
>the SWR, it wasn't too close to the published curves, especially
>on 15M.
>Anyone have similar experiences? What did you do?
Chad,
I have a kt34xa that was assembled according to the factory
dimensions. The swr is so flat across the band that I wouldn't
consider tinkering with the element lengths. The gain seems to
be very good.
However, your experience on 15 meters has been reported by
other KLM owners. The source of the problem has never been isolated.
In fact, the kt34xa that was tested by K7LXC and N0AX exhibited a
similar problem. The gain reported by Steve and Ward on that
antenna was abysmal on the high end of 15, and the f/b ratio
was a negative number! Obviously, something was radically wrong
with their sample, and something similar may be wrong with yours.
By way of comparison, here are the swr measurements on my
XA, and the swr measurements on the XA tested by K7LXC and
N0AX. Measurements were taken at the shack end of the feedline,
and the feedline lengths and losses were about equal.
freq mine K7LXC/N0AX
14025 1.6 1.7
14100 1.5 1.7
14175 1.5 1.8
14250 1.5 2.3 <--
14325 1.7 3.4 <--
21025 1.5 1.5
21125 1.5 1.6
21225 1.6 2.3 <--
21325 1.5 3.1 <--
21425 1.6 3.7 <--
28050 1.6 1.5
28250 1.4 1.6
28450 1.4 1.8 <--
28650 1.4 1.9 <--
28850 1.4 2.1 <--
28980 2.0
Here are a few places to start investigating:
1. Do your swr measurements with a conventional swr bridge,
rather than a low-power analyzer which may be subject to error
from external rf pickup.
2. Using an ohmmeter, measure the dc resistance from the outer
shell of the 10 meter capacitor to the outer shell of the 15
meter capacitor on each element half. It should be less than
about 0.5 ohm if all connections are clean and tight. This one
measurement tests every connection in the element half. Remember
to subtract the resistance of the ohmmeter leads.
3. Here's a hint from Jim, N6IG:
"I realized that if you were to measure the DC
resistance between the element halves of the rear
driven element, you should see a DC loop along the
straps, out the front driven, up the matching bars
and through the balun coil."
4. Make sure that the phasing straps are not shorting
to each other or touching the boom or anything else,
with the antenna in the installed position. Make sure
the phasing straps are secure, and that the swr does not
undergo major changes when the straps are flexed with a
broomstick.
5. Try replacing the balun with another 4:1 balun, or try
putting a 200 ohm resistor across the balun, and seeing if the
swr on an analyzer comes out to 1.0 across the bands.
It sure will benefit a lot of KLM users if you are able to
carefully isolate the source of the problem and report on its
solution.
Best of luck, and let us all know how it turns out.
Dave Hachadorian, K6LL
San Diego, CA
K6LL@juno.com
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