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[TowerTalk] Re: Re: Antenna element vibration damping - How

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Subject: [TowerTalk] Re: Re: Antenna element vibration damping - How
From: (Jan Erik Holm)
Date: Mon Aug 11 13:22:49 2003

Jiri Sanda wrote:
> Hi
> Exactly that is it.
> We have made elements with steep and slow taper. with long and short 
> thick section, light and medium heavy (25-38mm tube in the center of 20m 
> element)......all of them vibrated in "low" winds, "higher" winds 
> usually do not represent significant problem. I have bought the smart 
> book from Jim Leeson with the idea that someone much smarter then myself 
> will produce some scientific method how to eliminate this problem, well 
> his advice on the end is something like: vibration in a low wind is a 
> problem - use some rope, or cable and experiment......
Just came to think of one thing. Since I?m using double tubing in the
center it might act like a damper of some kind. Actually the inner tube
goes right thru the other tube and then there are spacers in betwen
to fix a good fit.
However on the 15m and higher bands I just have single tubing and they
don?t vibrate either so whatever........
> What I have observed - as said earlier is that if the tower is "sturdy" 
> i.e. does not move in the wind the antennas vibrate less too. I think it 
> is understandable since the movement of the tower gives it's kinetic 
> energy to the elements.... If you have "thin" tower put the antennas as 
> close to the guy-point as possible - it helps a bit for sure.
> 73 !
I have most of my antennas on 2 rotating towers and they aren?t really sturdy
at all. sure in light wind they will not move but when it starts to blow good
they will move a slight bit due to give in the chain drive, also there would
start to be some torque twist in the tower itself.
So this doesn?t go hand in hand with what you have found out Jiri, beats me!
> Jiri

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