On 1/13/2013 11:05 PM, john@kk9a.com wrote:
I had good luck with Yaesu G-2800 DXA rotators in Aruba, however once removed
from the tower the corrosion would lock them up. I am guessing that the
constant trade winds causing the antennas to rock back and forth kept things
loose. Do you have a corrosion problem in your part of Thailand?
----- Original Message -----
From: Charles Harpole
To: john@kk9a.com ; towertalk towertalk
Sent: Monday, January 14, 2013 01:50
Subject: GA-3000 found, tnx
This item is often hidden under "Accesories, general" title or is with the
rotors accessories.
I am awaiting my order final confirmation. So, likely I will have one soon.
For those who are wondering, this item GA-3000, made by Yaesu, mounts under the rotor
and above the rotor plate to provide a little bit of "wiggle room" for the
rotor as it lines up with thrust bearing(s) above it. This alignment is a constant
problem with large arrays, especially with lots of straight line wind pressure on the
mast. I have had problems with alignment with two of my towers in the past, one with one
thrust bearing and the other tower with two bearings.
Something to remember about towers and antenna systems.They ALL have
resonances in whole and in each part,
Antennas, masts, rotators, and towers. Each part and in combination all
have resonances.
Anything you do to the system changes the overall resonance. Normally
adding a longer mast, or something like this absorber lowers that
natural frequency, making the resonance fall closer to a natural point.
Often adding a shock absorber is as likely co cause a resonant point
that can be excited/driven by the wind as it is to improve things.
Vibration damping is as much an art as it is science. I've worked with
damping analysis and system and it can be quite a chore although "Bitch"
is primarily the word that comes to mind.. If you only have a small to
medium tribander, the mass is small and it's less likely to be a
problem, but with large antennas, or systems with a long mast between
the rotator and antenna, or a long boom, adding anything with a "springy
give" is dangerous and unpredictable. It may protect the rotator from a
premature break engagement, but it may add a resonance that will cause
the antenna, tower, or rotator to fail. For that reason I do not like
absorbers added to systems. To get the proper effect, the absorber
pads need the proper resiliency or they can make things worse.
Often, even with analysis, the only route is to try it and see what you get.
Proceed with caution!
73 & good luck,
Roger (K8RI)
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