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@arrl.net
>web: http://www.k1ttt.net
>AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>
>
>
>
>_______________________________________________
>
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>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
>
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