In a message dated 97-03-24 12:36:52 EST, you write:
> Thanks for the information. I will try to get some carbon steel schdule 80
> masting here. One of the weld shops here has a pretty good supplier. As
> far as where I was going to mount the rotor....about half way down the
> section. I gues you use some good old words and stick it in there. Would
> be nice to have it at the top where it wouldn't be such a hassle, but I
> think that it might bode better for the rotor to have it lower. I don't
> know...I am just a shade tree mechanic here....but I was thinking about
> way down the top section.
Lower mounting does a couple of things. It allows the longer mast to
act as a torsion bar to absorb some of the wind-induced torque. Imagine how
much torque a 30 or 40 foot internal mast could absorb, thus relieving some
(most?) of the load from the rotator.
Lower mounting also allows you to lower the center of gravity of your
mast/antenna system. It also decreases the bending moment on your rotator
(by having less mast sticking out the top); this may be a minor point. On
the other hand, imagine a 20 foot mast system with 18 feet sticking out of
the tower with antennas attached with 2 feet of mast in the tower to the
rotator. Talk about a BIG pry bar on the rotator! More mast in the tower
decreases this effect.
Having the rotator shelf in the direct vicinty of a guy attachment point
means that the wind torque that manifests itself at the rotator will be
transfered immediately to the guys with a minimum of intermediary twisting of
the tower. That's non-engineering talk but I think you get the idea.
Any other pluses? Or minuses? Further TowerTalkian input solicited.
73, Steve K7LXC
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com
Sponsored by: Akorn Access, Inc. & N4VJ / K4AAA