[TowerTalk] Wind Noise

[Grant Saviers]

I think there are different physical events being confused in this thread.

The rope or cylinder helix wrapped on a cylinder is designed to prevent 
vortex shedding which induces oscillations in a slender cylinder. 
Installed on tall chimneys, power lines, flag poles, etc.  The pitch is 
usually quite large relative to the diameter of the cylinder being 
protected and the diameter of the helix wrap is much smaller. google 
vortex shedding.  The small effective diameter increase from the wrap is 
probably a very small change wind load or ice loading.

The other is means to dampen an oscillation in a slender tube.  Way 
back, the Telrex TH7DX placed polypro ropes in the tips of the dual 
driven elements. The loose rope bouncing around inside dampened the 
oscillations enough so the elements didn't fatigue fail.  There is no 
"safe threshold" stress in aluminum so small motions repeated endlessly 
will cause a failure. I have personally verified this with a vertical 
that sang loudly.

I doubt that the vortex shedding wrap can provide any significant 
dampening.  It would need to be strongly bonded to the tubing and have 
substantial dampening properties.  Loose inside the tube was proven to 
work on TH7's.

Given the wind turbulence around lattice towers, I'd bet that sustained 
"tower" audio vibration is induced from antenna vibrations.  House 
mounts can be noisy just from looseness in the mounts.  Shock/vibration 
isolators might help reduce the coupling to the house structure. (many 
choices at McMaster).

In most structures, an ounce of vibration prevention (or good design) is 
worth 10# of cure.  (which is hard to do).

Grant KZ1W