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[TowerTalk] I: SWR Problem with 80M2.

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Subject: [TowerTalk] I: SWR Problem with 80M2.
From: Maurizio Panicara" < (Maurizio Panicara)
Date: Sat, 28 Aug 1999 00:47:39 +0200
Stll in trouble with his antenna, IV3TAN asked me to post his
message to the Tower Talk reflector hoping that someone can
help him.
If possible send answers directly to him
and not to me or to this reflector where he's not subscribed.

Mauri I4JMY

-----Messaggio Originale-----
Da: Alberto Annesi [IV3TAN]

I hope that you'll undestand my poor English!!!

My name is Alberto Annesi (IV3TAN) and about
2 months ago i bought a second hand (but new!!!) 2 element for 80 meters
the 80M2 model,  with the optional high power balun (10 kw).
I changed the SO239 female connector with a 7/16 professional connector
I assembled the antenna with extremly precision like a manual described.
After one mounth we put the antenna on top of the tower (@110 ft) but....
the SWR on 3.780 MHz and 3.525 MHz was very very high.
I measured the SWR after a section of half wave 50 ohm cable ( x velocity
factror) with
my Autek Research RF-1.
I measured also the SWR after a section of one wave 50 ohm cable ( x
velocity factor)
with my RTX Icom.
Both instruments gave me the same results:
at 3.525 MHz and 3.780 MHz the SWR was about 4:1
at 3.640 MHz and 3.890 MHz the SWR was 1,1 : 1   !!!!  100KHz more than the
right Freq.

After these tests we decided to measure the front to back and front to side
A friend of mine have an half-wave, horizontal 80 meters dipole @80 ft/h
2 miles far away, and from top of my tower you can see his antennas.
at 3.525 MHz and 3.780 MHz the F/B was 2 S-units (10/12 dB ...good) and
                                                 F/Side was over 6 S-unts
(30/36 dB ...good).
                                            on CW 3.525 MHz frequency the S9
dropped to S0....
When i trasmitted (with the antenna tuner) the results were the same.

at 3.640 MHz and 3.890 MHz the F/B and F/S were absolutely poor.  No F/B and
                                             only few dB of front to side.

At that time, i thouhgt that the measure of the antenna had to be correct
but i tried
another solution.
I changed the position of two bridges of the linear loading of the radiator.
About 12 in. for each part. The SWR at 3.525 and 3.780 was  perfect 1,1 : 1
i didn't have any Front to Back and Front to Side Ratio.
So i put two alumin stubs of 24 in. in the final section of the reflector
the result was the same: NO F/B and very very poor F/Side.

I think that the original measure (like a manual describe) are OK but i
that i have a problem with the impedence of the antenna.
If i change the lenght of the hairpin ( in the last 10 in.) i don't see a
alteration of my value.
 I pulled up and pulled down the antenna a dozen of  times.

Many thanks.  Alberto Annesi IV3TAN

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