My KT34A went up in 1985, worked well until about 3 years ago. Over the
past month I managed the logistics to lower it and refurbish it using
the m2inc kit. Its back up and now working well enough, but the result
and the experience is not what I expected. Maybe the info below will
help someone, or maybe I am very last KT34 owner that will ever attempt
an upgrade.
The good news is that the upgraded antenna is mechanically beautiful and
far more sturdy. I have every reason to believe the new capacitor caps
will have longer life than the OEM ones. This antenna will likely
outlast the old one, but I don't expect to live to 100 years old to find
out.
My search of the towertalk archives shows that the upgrade has been
available for about 15 or even 20 years. Some have reported issues, and
15m behavior seems to be the favorite complaint. That is not what
happened to me. I am focused on the SWR curve (the only easy measurement
to make), which is plausibly close to the 1985 KT34A manual's curves on
20m and 15m, but on 10m, when measured at the balun with the antenna at
25ft on the tower, the best I have achieved after the upgrade was 2:1,
nearly flat at that value from 28MHz up past 29MHz. I am calling it
"working well enough" because my criterion was 1.5:1 or better in the
shack on the frequencies I want to operate. My 150ft of coax lowered the
problematic 2:1 at the balun to 1.5:1 in the shack. Its a "big deal" to
bring the antenna down again, so that is what I will operate with. I
have no idea what is affecting the 10m SWR and I will not attempt to it
modify again until and unless I have a plan with some serious reasoning
behind it. (That is, I am not going to pay the day rate for a boom lift
again just to evaluate guesses.)
What I expected of the upgrade project was something akin to my
experience when I first put up the KT34A. In 1985, I assembled it to the
specified dimensions, measuring every dimension at least twice on the
ground. I got some help to gin-pole it to the 25ft level on my cranked
down 1963 model guyed TriEx 88ft tower. The SWR was below 1.5:1 across
all three bands and stayed that way for more than 30 years. For what its
worth, prior to 1985 I spent a day as one of a team of college students
that put up a KT34XA at the club station. I recall the experience being
about the same: measure carefully, put it up, and pour RF into the coax,
and that is why I chose the KT34A for my home station.
The upgrade experience was different.
I started the project earlier this month by using a boom lift to take
down all the elements including their clamps. I left the boom on the
mast. Essentially all the original plastic capacitor ends (mine were
green) had cracked, one of the aluminum straps had broken at its
clamping screw, and bugs had built stuff inside much of the 3/8" tubing.
It took several days of hammering aluminum with a plastic mallet, and
some work with a punch and hammer (some of which was destructive) and I
managed to finish the tear down with enough aluminum tubing to apply the
upgrade and have a complete parts list. Almost. I had to order one 10"
length of 0.75" tubing because the original had a very deep dimple in it
that I can only imagine was made by a .22 caliber bullet. Or a hawk with
a very tough beak. I also discovered a cracked boom-to-element clamp
(its amazing that DXEngineering sells a mechanically compatible part set
after all these years. Read their fine print; to replace the KT34 clamp
assembly, you have to order three items: the clamp, the size-adapter
halves, and the 3" "hose clamps." Thank you to overnight FedEx to keep
me on schedule.) The old balun checked good on the antenna analyzer but
rattles when I shake it. Thanks again to DXEngineering for having a
suitable substitute. (I had to design and 3D print an adapter bracket to
make their square peg balun fit in the KT34A's round balun hole. photo
on the link below.)
Here is where things didn't quite go as expected.
The 10m SWR using the manufacturer dimension specs was unacceptable. I
rented the lift a couple more days. First I took element tips down to
triple check all the dimensions, disassembled and cleaned out the
capacitor tubes again (as they cannot be inspected from outside.) Put it
back up. Zero change in SWR. Finally, I turned to "tuning" the 10m
shorting bar positions per recommendations from m2inc. The result is a
just-barely-acceptable 10m curve. Aside: per m2inc's recommendation, I
ran the analyzer directly at the antenna separately with the old and new
baluns. SWRs matched on the two. The old one is probably still good, but
I am not putting it up when it rattles.
I have put a couple of documents on this web page to describe some of
the measurement detail: http://wew.w5xd.net/kt34a
It remains possible that I misread instructions, or that I am
incompetent with a tape measure. But I believe something else is the
cause. I do not blame m2inc. They don't have a supply of worn out KT34's
to test.
Wayne, W5XD
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