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[email protected] · October 18th 06, 09:46 AM posted to rec.radio.amateur.antenna

Hi Gene,

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

Hi Francesco,

You did not describe the vibrations, so this may be off base. If it is a
"sound", then perhaps the tubing is acting like a flute. Plugging the
ends of the open tubes would stop the sound. It may be necessary to
leave a small hole for drainage.

The sound is low frequency, I'd say less than 100 Hz with amplitude
modulation of 1-2 Hz probably
due to boom vibration. I thought about flute effect but I think it
would be an higher pitch in that
case. I read many interesting suggestions though, I hope to be able to
try some of them in the next
week end.

73

Francesco IS0FKQ/I8