Fill it with expanding foam used for heat insulation.
Art




Bob wrote:
Lots of commercial antennas come with rope inside the elements for
mechanical damping. Just find some dense and preferably synthetic rope
that just fits inside the elements. If it's a vertical antenna, cap the
top elements to keep rain from entering, otherwise leave the elements
open so any moisture will bake out in the sun.
Bob


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