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John Ferrell · October 17th 06, 03:52 PM posted to rec.radio.amateur.antenna

On 17 Oct 2006 03:01:52 -0700, wrote:

Hello all,
I build one year ago an 8 element 50 MHz yagi. Boom is made with 50 mm
square aluminum tubing with
a second square tube on the center of the antenna to strenghten the
boom. Elements are made with 20 mm
round aluminum tube in electrical contact with the boom. The antenna is
a good performer but it has one
problem: it sounds even in light wind and vibrations come down the mast
and are very annoying in the whole
house. The worst problem is that resonance succeeded in unscrewing the
rotor bolts. I'm going to use a
special for bolts and screws but I'd like to find a method to avoid
mechanical resonance of the antenna.
Does anyone know a good method? Would it be better to add two insulated
pulling wires at both ends of the boom (even if probably also elements
produce udible resonance)?
Thanks in advance

Francesco IS0FKQ/I8
It sounds like a really stable mechanical design.

The first thing that comes to mind to me is to damp the vibrations. A
spiral wrap of something soft like rubber tubing on the boom and the
elements. Unfortunately it would add both weight and wind resistance.
Also it would contribute to maintenance. I doubt it would weather
well.

The next thought is to try some soft sleeves randomly placed on the
elements and boom. I would be inclined to use chunks of tubing about
75mm (3 inches?) long and secured with cable ties protected with black
tape. Splitting the damping tubing should make it easy to install.

End caps on the elements and boom are a given but if drains are not
provided for each instance water will collect and burst the tubing by
freezing.

I hope you have an easy way to get at the antenna for experimenting!
John Ferrell W8CCW

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