[TowerTalk] KT-34XA tuning (long)
Jeff Singer
k2kv@reallybig.com
Tue, 22 Sep 1998 18:41:57 -0400
Chad -
I've built (and rebuilt) a number of kt-34A & -XA antennas, and have always
enjoyed superb swr and performance. Besides the problem of occasionally
having to dip the tubes into the pool to get everything over to the tower,
the only difference here is that I NEVER tested them pointing up! You might
find that, once it is horizontally mounted, it will harmonize with its
environment in a much more acceptable manner.
Remember, taking readings while the antenna is vertical only gives you an
"approximation" of how things will be once installed properly. If you had,
for example, NO resonance on one or more of the bands, you would want to
know this before going to the trouble of mounting the beast.
Small changes in resonance can be expected for an antenna that is designed
to be horizontally installed at 60 feet, but which has been installed
vertically at 9 - 15 feet instead. If it were me, I'd reset all dimensions
to exact specs in the manual, and put the thing up already. Then you'll know
for sure.
But don't simply trust me (I am not that smart). Wait until one of the
accepted gurus tells you the same thing. :-)
Good luck.
73,
Jeff K2KV
k2kv@reallybig.com
http://reallybig.com - "The Complete Resource for All Web Builders"
-----Original Message-----
> From: owner-towertalk@contesting.com
> [mailto:owner-towertalk@contesting.com]On Behalf Of WE9V Chad Kurszewski
> Sent: Tuesday, September 22, 1998 5:02 PM
> To: towertalk@contesting.com
> Cc: k7sv@juno.com
> Subject: [TowerTalk] KT-34XA tuning (long)
>
>
>
> 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.
>
> The antenna:
> KT-34XA
> Brand new Blue Insulators installed
> ALL connections (strap, cap tube, tubing) thoroughly cleaned & penotroxed
> All dimensions set, checked, and REchecked to latest dimensions
> I've read the K3MM "bible" to rebuild
> I've check the balun with the MFJ-259B and get nearly a 30dB return loss
> into a 200 ohm load on all bands. (That means less than 1.1:1 SWR.)
>
> The test setup:
> Antenna pointed straight up into the air
> Reflector off of ground by 9-15'
> Elements in a plane 90 degrees to tower (perpendicular to a line drawn
> from boom to tower)
> Brand new RG-213 coax, cut to 0.5 wavelength on 7.15MHz
> (multiple of a half wave for 10/15/20)
> New MFJ-259B
>
>
> The results:
> 13.875 3.0:1
> 13.93 2.0
> 14.0 1.4
> 14.1 1.1 No complaints here.
> .
> .
> 14.35 1.1
> 14.44 2.0
> 14.46 3.0
>
>
> 21.00 3.5 This sucks!
> 21.018 3.0
> 21.070 2.0
> 21.1 1.8
> 21.2 1.3
> 21.3 1.0
> 21.4 1.0
> 21.62 1.3
> 21.696 2.0
> 21.75 3.0
>
> 27.8 3
> 27.966 2
> 28.0 1.9 Not great.
> 28.1 1.6
> .
> .
> 29.06 1.1
> 29.25 2.0
>
>
> So, I've hoisted this thing up in the air (by myself) NINE times,
> each time changing the tuning a little bit.
>
> The goal was to adjust dimension C (10M) and B (15M) to get the SWR
> down on the bottom of those bands and see what effect that has on 20M.
>
> Starting with the reflector (according to KLM's "the horse's mouth",
> the reflector has the greatest influence on the bottom of the band),
> I lengthened C and B. Only small improvements. I then went to the
> 1st driven element (the longer one, which has more to do with the
> bottom of the band) and adjusted B and C. Small improvment.
> Next to the first driven and then the first director.
>
> I now have B and C maxed out on both the reflector and the 1st driven.
> (B=47.75 on ref and 48 on rear drvn)(C=28.25 on ref and 27.75 on
> rear drv.)
> Both 10 and 20M have better SWR across the band but on 15M the 2:1 point
> is still only at 21.030.
>
> I then started to adjust (lengthen) D, which makes all 3 bands get
> "longer"/lower in frequency. I lengthened reflector D by 1" and
> now 2:1 is at 21.007. Lengthened it by a total of 2.5" and now
> 21.000 is 1.9:1. My last straw was to lengthen it all the way to
> 3.5" longer and lengthen the rear driven by 1". That resulted in
> a 21.000MHz SWR of 1.7:1. 10M is 1.2:1 max from 28-29.1, and 20M
> is 1.2 max for the whole band. The top of 15 is 1.1:1.
>
> I'm out of knobs to tweak. Where do I go from here?
> KG9X also rebuilt one and built it to book specs and the SWR was
> perfect.
>
> Anyone have similar experiences? What did you do? Wasn't there
> someone on the list that measured the resonances of each of the
> elements? Larry, K7SV, you have those? I'm thinking that one of
> my elements is way off for some reason and that data would help.
>
> Help!!!
>
> Thanks,
> ---
> Chad Kurszewski, WE9V e-mail: WE9V@qth.com
> The Official "Sultans of Shwing" Web Site: http://www.QTH.com/sos
>
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