[TowerTalk] Re: Antenna element vibration damping - How

[Jiri Sanda]

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......

Concerning rope-cable. My experience is it helps always - if it does not 
help use something heavier - like old 75 Ohm coaxial cable...... That is 
always ultimate solution provided the element can take it.

We have not made extremely thick elements since it is very expensive and 
to put in some "rope" is much more efficient money-wise, so if this is 
the case ????

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 !

Jiri
OK1RI


David Robbins K1TTT wrote:

>>Jiri Sanda wrote:
>>,>
>>    
>>
>>>To later responses.
>>>Jan - I would like to see some designs that DOES NOT vibrate at all.
>>>Until now I have not seen such a beast !!!
>>>To kill the vibration with some rope or wire is fairly easy and does
>>>      
>>>
>not
>  
>
>>>represent any significant cost or problem to put in.
>>>
>>>      
>>>
>>Yes I know. The first Yagi I built 30 years ago lost the elements
>>    
>>
>after
>  
>
>>just 2 weeks due to vibrations/resonance, was then fixed with ropes
>>    
>>
>since
>  
>
>>at that stage I didn´t know better.
>>These days I don´t need ropes since my elements doesn´t vibrate.
>>    
>>
>
>Have I missed it, or have you ignored the question???  In any case here
>is the basic, very basic, question again:
>
>How do you design elements so they don't vibrate?
>
>
>David Robbins K1TTT
>e-mail: mailto:k1ttt at arrl.net
>web: http://www.k1ttt.net
>AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> 
>
>
>
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