In a message dated 99-02-16 08:25:28 EST, k4oj@ij.net writes:
> every time I see those pictures of a Telex rotor on a pipe mount (that
> piece attached to the bottom of the rotor grabbing a vertical pipe for
> mounting) and then a mast with an antenna on it above the rotor I cringe...
>
> the only thing I do not like about out of tower (tree) rotors
> is that there is nothing to hold onto the mast if you don't have the rotor
> there...on a tree this is extra crucial.
>
> the ongoing debates as to whether or not two thrust bearings on a tower all
> point to the stability achieved by having two points of stability for your
> mast far outweighing one certainly quantum leap when you have nothing
> stabilizing a mast above rotor....if you mount to a tree in my opinion you
> might as well marry a top section of tower to the top of the tree as a
> means to obtain this stabilizing your mast really outta have!
>
The reason that you would have two thrust bearings is so that the mast
is held securely in the event that you have to do a rotator swap. This is
particularly handy with a big mast and a stack of antennas where the center of
gravity is above the top of the tower.
I mast-mount tree installations all the time and prefer the TailTwister
because of its added physical strength over the Ham IV. When I was at Hy-Gain,
we destruct tested a T2X with a lateral load to see what it would take. It
finally broke right at the neck just above the top bell housing at a force of
3,000 ft.lbs. That's magnitudes over what you would encounter with a typical
small to medium sized HF yagi mast mounting situation. It's plenty strong
enough for mast mounting.
If anyone is interested in a write-up on this test along with lots of
other rotator information, my 3-part reprint from my "Up The Tower" column is
CQ Contest magazine is available for a buck from Tower Tech, Box 572,
Woodinville, WA, 98072.
Cheers, Steve K7LXC
Tower Tech
Champion Radio Products
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