Dana,
Can you describe the vibration in more detail? Do you mean it sways back and
forth at the top? If the guys are adjusted properly, this shouldn't happen
-- the mast should be dead still even in very high winds.
The first thing I would check is the guy anchors. Make sure they haven't
shifted or pulled out of the ground. If they have, then the guys are too
loose and the mast will sway. Which anchors did you use? While the short
ice-and-rock anchors are pretty good, I probably wouldn't use them in a
permanent installation. The screw anchors need to go all the way in, so that
the eye is flush with the ground. If you have sandy or loose soil, neither
type of anchor will work and you may have to consider embedding the anchors
in cement.
Once you are sure that the guy anchors are not able to move, make sure you
have sufficient tension on the guy wires. If you pull on one of the top guy
wires and the mast visibly moves, then the guy wires are not tight enough.
The procedure is to manually take up as much slack as possible in each
snubber by unlocking and pulling any excess guy wire through. Do this in
equal amounts for each snubber so that the mast is as close to vertical as
possible. Then tighten the large nuts on the snubbers a few turns at a time,
going from guy to guy to ensure that the mast stays vertical. I usually
tighten the snubbers until I can't turn the nut with hand pressure. I
usually test the guy tension by taking a section of wire between my thumb
and forefinger and "tweaking" it. There should be some movement, but very
little -- maybe 1/8"-1/4" max. At any rate, once the guys are properly
tensioned, the mast won't move. Note that if the snubber nuts don't move
freely, you may have one or more defective snubbers. With no tension on the
guy, the snubber nut should rotate freely from one end of its travel to the
other. I have some snubbers that won't move in one direction due to some
sort of mechanical defect (still investigating that.)
If the guy anchors did not move, then perhaps the sections were not put
together correctly. I'm not clear on what you mean by the sections not
mating perfectly. I can't imagine how this could happen, unless the flanges
on your tubes are severely damaged. Each section has a small square "key" in
the flange at one end, and a mating small square hole at the other end. When
two sections are put together, bottom to top, the key at the bottom of the
upper section fits into the hole at the top of the lower section. Also note
that the key at the bottom of the very lowest section fits into a slot in
the elevator. This allows you to rotate the tower from the bottom. If you
put two tops together or two bottoms together somewhere along the line, they
wouldn't have fit properly.
The key and slot must be lined up perfectly in order for the sections to
mate properly. When they do, there is no space between the flat portions of
flanges. Sometimes it appears that the sections won't go together completely
and there's a small space between the flanges. This means you don't have the
key and the slot lined up perfectly. You have to lower the elevator
slightly, rotate the new section so it mates properly with the section above
(key in slot), the raise the elevator until the flange faces are flat
against each other. Keeping tension on the winch, you then slip the ring
clamp over the assembly and snap it shut. If you hoisted the mast with some
sections not mated properly, it's conceivable one of them slipped into place
by itself, reducing the tension on the guys enough to cause the vibration
you are seeing.
If you think you may not have mated the sections incorrectly, lower the mast
as soon as the winds are calm (< 5 MPH) and correct this.
If you have any other questions, feel free to ask. (BTW, I have a 50-foot
AB-577 with a Force-12 5-el 15M beam with Ham IV rotor -- probably very
similar to what you have -- and it's solid as a rock.)
73, Dick WC1M
> -----Original Message-----
> From: Dana Roode [mailto:dana.roode@gmail.com]
> Sent: Sunday, June 19, 2005 8:57 PM
> To: towertalk@contesting.com
> Subject: [TowerTalk] AB577 Vibrations
>
>
> AB577 Owners/Experts -
>
> Thanks again for all the input on my previous question about
> mounting a rotor on my AB577. I was missing the "mast
> adaptor" and got one from K4TMC - works great.
>
> 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
>
>
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