[TowerTalk] GA-3000 found, tnx

[K8RI]

On 1/13/2013 11:05 PM, john at 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 at 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)