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
|