My thanks for the input on my AB577 vibrations, and my apologies for
not getting back to the topic sooner.
I put my AB577 up using new 3/16" cable with turnbuckles, clamps and
what not. The cables that came with the mast were not in good enough
shape to use, in my opinion. I am not using the earth anchors either,
as I already had a set of large diameter steel pipes cemented in the
ground as anchors from a previous project.
I tightened the guys some more when I got out to the QTH last time,
and that may have helepd with the vibrations. The mast is not visibly
moving, and there is no apparent sign its about to go down. The
vibrations are like Bob Allen wrote about below - all of the sections
are lined up properly with the keys in the right places, but there are
very small imperfections in the mating of the sections and that seems
to result in the vibrations. I can''t tell which joint is loose, or
if several are, from my observations.
It is possible that one of the clamps isn't working like it should,
although they all seemed fine when I put the mast up. This is
something for me to check.
For now, its up, and withstanding our routine 30mph+ winds.
Thanks for the input everyone,
Dana
On 6/22/05, Bob Allen <mcamp@gmavt.net> wrote:
> Here is what we learned at FD testing:
> The joints between the mast pieces varied as to tightness, some very
> tight and some had a bit of slop. It didn't seem to matter which clamp
> we put on them, the loose joints were loose.
> We test fit all the pieces by trying every tube with every other tube
> until we found as many tight joints as possible, then we numbered all
> the sections and wrote "shim" on the loose joints. of course the towers
> are assembled in order now.
> We made shims that eliminated the looseness. .005" brass, these were
> used in any joint that wasn't tight, works great.
> Why did we care, you may ask?
> When you put these up at FD the wind has an effect that causes a certain
> amount of anxiety about the whole thing coming crashing down, we found
> that stiffening the joints made it much easier to keep the tower
> straight while erecting it.
> We have one tower with 12' of 1.5" mast on top af tower with a Mosley
> Senior 2' from bottom of 1.5" mast and a 15' spreader at top that holds
> up some wire antennas. The other tower has the same mast above top with
> a 20 and a 40 meter yagis spaced 9' apart.
> Last year we had a 50+ mph windstorm come through and the towers didn't
> even dance around, the antennas twisted some but nothing serious.
> We applied this fix to another tower that owned by a club member who
> used it for field day and went through the same storm at 1700' above sea
> level no problems.
> Bob
> KB1FRW
>
> Jim Jarvis wrote:
>
> >Dana wrote:
> >
> >I put my AB577 up today at 45' with a 5 element 15meter beam on top.
> >Ive noticed it vibrating in the wind (it did this when I had it up
> >without the beam as well). Some of the top sections of mast shake
> >around - I figure this has something to do with the fact that the
> >sections of mast dont mate perfectly. Its hard to see, usually I just
> >hear it.
> >
> >Should I worry about this? Does your AB577 do this in 30mph winds?
> >Dana
> >-0-
> >
> >Dana:
> >
> >In a word, NO.
> >
> >I suspect you may have insufficient upper guy tension...or possibly
> >that the clip-rings which hold some of your sections together are
> >stretched out, and not clamping tightly. If the latter is true,
> >try Ben at Ontario Surplus for replacements.
> >
> >N2EA
> >jimjarvis@ieee.org
> >
> >_______________________________________________
> >
> >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.
> >
> >_______________________________________________
> >TowerTalk mailing list
> >TowerTalk@contesting.com
> >http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> >
> _______________________________________________
>
> 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.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
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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