[Antennas] Vibrating hollow elements

[DJED1 at aol.com]

Tho I'm an electrical engineer I ran across this problem years ago in one  of 
my antenna designs.  The mechanical engineers identified the vibration  
problem as one induced by vortex shedding when air flows over the element.   While 
one solution is to damp the vibration, another is to break up the  vortex.  I 
was reminded of the problem when I got my new car a  few years ago- the 
antenna had a spiral filament wound on the cylindrical  antenna shaft.  I've seen it 
on several car antennas, so it must be  effective in eliminating the vortices 
that cause vibration.  While getting  the antenna down may not be easy, 
wrapping some twine or wire along the elements  may solve the problem.
Ed  WB2LHI