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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