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[TowerTalk] Re: rope in elements

To: <>
Subject: [TowerTalk] Re: rope in elements
From: (
Date: Thu, 29 Mar 2001 09:02:16 EST
>  I'm not worried about the vibration because it is steel. I did know of 
>  a fellow with an aluminum tower who lost the whole top 30 feet or 
>  so of the tower in a mild breeze, because it vibrated and cracked.

Material has nothing to do with it. Steel will fail too, it is the matter of 
time, or better to say number of cycles. 
To underline the mechanism of failure, it is not from say vibration exceeding 
the material strength, it is from cyclical stress, aggravated by grooves, 
scratches and it is microscopic failure. In aluminum, material hardens, 
crystallizes, fracture starts at the point of surface scratch (or not) and 
starts slowly propagating across the cross section of element. Eventually 
breaks with clean, sometimes even shiny cut.

The point is, anything mechanical has some resonances somewhere, question is 
how and where it is mounted. It starts with tower foundation, tower, guys, 
masts, plays in the system, other antennas, rain droplets, owls, lawyers, 
etc. Just picture tuning fork and see what affects the tone, same goes for 
antenna installation, it is a giant tuning fork, as soon as you hear, see or 
feel vibrations or thing singing, go and kill it by dampening (ropes, things) 
because sooner or later fracture will come. The thing is that you can't even 
see the fatigue fracture in progress, unless you use ultrasonic testing. The 
result is piiiinggg... and part just breaks.

Things can vibrate in slight breeze or strong winds, it is just a matter of 
finding "happy" resonance point. Just like antenna modeling software, the 
mechanical vibration calculation software is not capable of encompassing ALL 
variables participating, and therefore fools would rely on it for absolute 
answers (I tried and got "burned").

Be suspicious if someone claims that their stuff is vibration free. It ain't 

So don't let it zing or vibrate, kill the vibrations and you will have long 
lasting antennas. It also does not mean that just sticking rope in the 
element fixes everything, you better make sure that that rope in that element 
dampens the vibrations, if it doesn't, try different rope (diameter, length, 
mass), just remember rope needs room inside of the element to jump and 
counteract the vibration of the element. 

As far as Force 12 warranty thing with ropes, I don't understand it. 

Yuri, K3BU

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