[Antennas] Vibrating hollow elements

[Jack Painter]

Ed, those were excellent comments - thank you for sharing this.

On the damping side, attaching a plain u-bolt (or two) along the supporting
mast might also tame the sympathetic oscillations. This could be tried
without taking down the whole antenna. String wound in a spiral on parts of
the antenna sound like a good plan if easier to accomplish efforts don't
solve it.

Jack


>From: 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