Hello Towertalkians.
I need help to resolve a problem with my new KT34XA antenna.
Before to put on my the next new tower, I try to set up and tune the
antenna on a
crack-up tower. I made the tune test at 20 feet, and later when I put
the antenna at
45 feet I dont note practically any difference.
My problem is as follow, with the factory dimensions, I found
practically perfect the
VSWR on 20 meter, its a two deep SWR around 14025 and second one around
14385,
and between this two points the SWR ratio was below 1.5 .
On 10 meters, its was a litle diferent, I found the two SWR low level
practically on the
factory curves, but it was i quit high on 28000 khz ( 1.5 , but in
order of factory
specifications ).
The problem appears on 15 meters.
I found the two low point of SWR, but the lower was at 20600 khz and the
up was in
21150, on any case more than 400 khz bellow factory specifications.
Reading the antenna manual, I decide to make a litle bit short the C
dimension on
the reflector , in order to get better SWR on low portion of 10 meters (
I shorted
1 inch ) and I shorted 2 inches the B dimension of reflector and
Director 1, in order
to move down the both ( DOWN and UP ) SWR ratio.
With this changes I dont observe any change on 20 meters.
I move, as I expected, a litle bit down the LOW END SWR on 10 meters.
But, on 15 meters ( remember that I short 2 inches on the Reflector an
Director 1 ),
the low end and the high end of SWR move around 200 khz. Then,
considering
that the High End SWR was OK ( it keep around 21350 ) and the LOW END
SWR
keep around 20800, I decided to short 2 more inches the dimension B on
the reflector,
in order to move up 200 khz the low end SWR. With this change the low
end of 20
meters move a litle bit up, but still bellow 1.5 SWR on 14000 khz.
Well, after this second change, no effects on 10 an 20 ( a litle on 20 )
is noted, and the SWR curve on 15 meter was more than acceptable. Bellow
1.3 from 21.000 to 21.400.
Then, you can ask ..., what's the problem ?.
Well the problem is the Front to Back ratio on 15 meters.
I made, with a good friend of mine, EA3CR, located 40 milles far a way
from my QTH,
and when all the bans was closed, several metering. I must note that the
S-meter of
EA3CR receiver is good calibrated.
The F/B result was :
28.000 15 db
28.100 20 db
28.200 31 db
28.300 25 db
28.400 20 db
28.500 24 db
28.600 22 db
28.700 13 db
with the best forward gain between 28.400 to 28.600
On 20 meters the F/B result was:
14.000 18 db
14.100 20 db
14.200 16 db
14.300 15 db
and the best forward gain around 14.200 khz .
NOW the surprise: 15 meter :
The F/B was :
21.000 -6 db (best signals that on forward direction ).
21.100 -4 db ( quite similar that on 21.000 ).
21.200 3 db ( now the foerward direction begun to work .... ) .
21.300 5 db
21.400 15 db
21.500 18 db
21.600 20 db
21.700 22 db
and we dont made more test up 21.700, but probably the best F/B must be
a litle up
21.700 khz.
I suspected, that made as short the B dimension on the reflector, this
acts as a director from 21.000 to 21.150, and acts real as reflector up
21.400 khz.
Have any KT34XA user , any sugestion to resolve this situation on 15
meters, and
mantain a SWR in good order from 21.000 to 21.400 ?.
I have no literature about the "2 drivers cell" of this type of
antennas, but I was
surprised that any of the driver element must be move to correct the
SWR.
Thank's a lot in advance
Fernando.
EA3KU.
BTW. In order to dont increase the bandwitch, answer direct to me and
later I
will send a compendium of the suggestions.
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