In a message dated 9/16/2006 9:02:29 A.M. Pacific Daylight Time,
>> I'm going to move my rotator to the bottom of my 80 foot tower and
> would like recommendations for the mast. I will support it at the top
> with a thrust bearing, and at least one, possibly two, non-thrust
> bearings part way down to prevent side to side movement.
> My question is what would be a good mast material? It would only have
> to support it's own weight and I'm wondering if 2 inch water pipe
> Remember this mast has to do basically what the top mast does. It is one
long torsion bar.
That and with a thrust bearing at the top the tower will end up supporting
all the extra weight of the masting.
Umm, I'll go with the long torsion bar. BTW, mounting antennas
alternately up a mast goes a long ways to minimizing torque since they'll
each other out. (Article in QEX or QST by Dick Weber, K5IU, PE.)
But the mast sticking out of the top of the tower is naked and is
subject to sometimes large forces. If an antenna one foot above the top of the
tower has x force on the mast, then the antenna up ten feet will exert 10x
bending moment on the mast; forces are becoming significant. Your captured
inside the tower doesn't have anything like that so you can use more
ordinary materials for this masting.
I'm not an engineer so can't give you any calcs or specifics
TowerTalk mailing list