Also, be aware that you MUST eliminate that
resonance ! Many years ago, myself (and
another ham) obtained the 6 meter moon bounce
array from a well known ham (he built it, got
echos, than abandoned it- reason, at that time,
he was the ONLY op capible of 6 meter moonbounce!
helped the owner of the first half put it up
on 5 inch irrigation pipe! The array worked well-
but the wind started oscillations in the elements.
The elements began to shear off from metal
fatigue, at the point where they went thru the
boom. Same happened to mine, even as stand alone
yagis! These had elements of 6061-t , 5/16 inch
dia. tubeing, if memory serves.
Translation: IF allowed
to continue, look for the elements to start
breaking off, at some point in time! Would agree
that the insulating foam might be enough to
stop the oscillations in the elements. Good luck
Jim NN7K

Gene Fuller wrote:

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.

73,
Gene
W4SZ