Let me trow in my expirence from last years ON5TN optibeam OB 16-3
installation.
Whe got some problem on 10m with this antenne ,sometimes good sometimes bad
swr when
moved the antenna up and down the testtower.
We found that 1 screw on the square feeding at the 10m driver was loos a
little bit.Thigten this srew
did the job.I don't like the square feeding system ,you have a minimal
contact with the element.
73
marc on4ma
----- Original Message -----
From: <Gary.Stone@med.va.gov>
To: <towertalk@contesting.com>
Sent: Wednesday, December 14, 2005 2:15 PM
Subject: [TowerTalk] Beam toubleshooting problem - help please
> Hi to all,
>
>
>
> I have a problem with a yagi and I am seeking your assistance and
opinions.
> I have a couple of people coming out to the
>
> station and I hope to gain some views here to share with them. First, the
> basic problem. On 40 meters
>
> the SWR will sometimes jump to about 3 to 1 from flat. I can make a few
> contacts and this does not happen but it
>
> will eventually. A quick turn of the antenna in any direction drops it
back
> to flat. I have made as many as two or three
>
> 10 minute QSOs before the problem hits again. Now, my setup:
>
>
>
> RG45G Tower, 80 feet.
>
>
>
> Optibeam OB17-4 right above top of tower (3 ele on 40, 4 on 20 and 4 on 15
> and 6 on 10 for 17 ele total - 39 foot boom square boom)
>
> The 3 elements on 40 meters have an 'air coil' but the rest are all full
> size elements.
>
>
>
> 12 feet further up on mast I have a Force12 WARC7 with 3 ele on 12, 2 on
17
> and 2 on 30 mtrs.
>
>
>
> Both antennas are fed with LMR400 Flex to a point down the tower and then
> continues with LMR400 into a coax switch (Array Solutions Rat Pak) at
>
> the base of the tower. Then a single LMR400 into the shack.
>
>
>
> OK, some facts that hopefully help with the troubleshooting.
>
>
>
> * This installation has been completed about 7 months and I have made a
> little over 800 qsos on 40 meters before the problem started.
>
> * I can't detect any change on the other 3 bands. NOTE: The OB17-4 has
> square tubing for the feedline to the 4 driven elements for the
>
> 4 bands. The SWR on 20, 15 and 10 seems good and consistent.
>
> * Turning the beam correcting the problem certainly seems to point to
> something loose in the 40 meter section of the beam. Well, we
>
> did find a loose bolt on the end of one side of the driven element for 40
> mtrs. Corrected that (that took awhile and two people on the
>
> tower) and then the problem continues.
>
> * The change that most recently occurred before the problem was that we
have
> had trouble with the feedline loop for the rotator off and
>
> on. And recently the coax got caught in something and became damaged.
So,
> the piece of LMR400 flex from the OB17-4 to to a place down
>
> the tower was replaced with another piece of coax cut the exact same
length.
> The coax was then rerouted to try a better way to make
>
> the rotator loop so that nothing was binding. I know this is the recent
> change just prior to the problem but it is difficult for me to think
>
> there is a feedline problem with the coax because the same run of LMR400
> feeds the other 3 bands on this beam and they are fine.
>
> * Connected an swr meter and radio directly to the coax at the base of the
> antenna with same results (sometimes flat and then
>
> sometimes shoots to 3 to 1 SWR). This bypassed the coax switch at the
base
> of the tower and all parts going to the shack.
>
> * The OB17-4 has a rectangle "termination stub" that is about 1 foot x 2
> feet and it serves to match the SWR for 40 meters.
>
>
>
> OK, since turning the beam corrects the problem temporarily (every time -
10
> our of 10 times) I would conclude a loose element or a cracked
>
> or otherwise damaged termination stub? We had hoped the one loose element
> piece solved the problem. Without taking down the driven
>
> element the driven element appears to be tight at all other joints. My
> question (among others) is "Can a parasitic element (perhaps with a
>
> loose connection in one of the telescoping sections) cause this problem?
If
> (for example) a telescoping piece of one of either the reflector or
director
>
>
> had an intermittent loose connection would that cause an SWR spike. (I
sure
> hope that is not the case as that would mean a bucket truck
>
> or a crane !!). I am thinking the next step would be to completely take
> down the driven element (do able) and make sure all connections are solid
>
> and then put it back and make sure the termination stub is good too. We
> have also thought about taking a long pole (would have to be 20 feet or so
>
> like bamboo) to the top of the tower and tap the reflector and directors
to
> see if we can get it to screw up consistently. Of course we can do this
>
> with the driven element also and the termination stub. Fortunately the
> termination stuff is easily reached from the top of the tower.
>
>
>
> So, thanks so much TT pros and any thoughts greatly appreciated. I am
> thinking it must be something limited to the 40 meter section of the
>
> OB17-4. Am I missing something?
>
>
>
> Gary, N5PHT
>
>
>
> Gary Stone, BA, LCDC
>
> Case Manager, Bonham DSAP
>
> Sam Rayburn Memorial Veterans Center
>
> (903) 583-6411
>
>
>
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
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>
>
>
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>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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