In a message dated 97-04-12 00:22:15 EDT, firstname.lastname@example.org (John D. Peters)
> I think the weight of the mast and antennas should be transferred to the
> tower through a very good axial and thrust bearing system. The torque in
> the vertical axis from wind load should also be transferred to the tower
> through another axial and thrust bearing system far enough inside the
> tower to handle the torque.
I used to think the same thing and thought I was prolonging the life of
the rotator by just having it turn the system while the dead weight was held
by the thrust bearing. That is, until it was pointed out to me by a
ham/factory facilities manager that these rotators were designed for some
amount of preload or weight on the rotator. The weight seats the bearings
and other transmission parts. For instance, the Orion 2800 says to put ALL
of the weight of the mast/antenna system on the rotator up to 1800 pounds.
Hy-Gain doesn't publish vertical load figures anymore but Yaesu does; how
much of this should be preloaded? The problem is that no one has been able
to give me an idea of what the preload figure should be OR how to determine
it. There are little machine shop devices that will deform at certain
weights and they could be used but I still don't know what the specs are.
Can any TowerTalkians shed some light on this?
> If you use an in line rotator, you should align the mast in the chuck so
> the center of the mast is at the center of rotation. If indeed someone
> sells a rotor with fixed chuck NOT designed for 1 5/8 inch water pipe,
> that is not a mast I would use. If you expect such a rotor, with an off
> center load, to rotate the mast (and antennas) and tilt/bend the mast as
> it rotates, and not damage the hole in the top of the tower, and support
> your system, good luck. (At least you could shim the thing to 2" diameter
> in the chuck.)
Can this be done by hams in the field and yield a reliable, non-slip
mast/rotator connection? So far, I haven't seen it. This and trying to
adapt/connect two different pipe sizes are consistently the most kludged
parts of tower installations. And they generally don't work for more than a
couple of weeks.
In case someone doesn't realize it, the Hy-Gain Ham IV/V and T2X are the
rotators with fixed mast capabilities. Most other rotators (Create, Orion,
Yaesu, etc.) use a two-piece clamshell type arrangement that'll take almost
any size mast AND allow you to center it.
> I think mast (and
> antenna) weight is a big issue. Strength of material, diameter and wall
> thickness of the mast is also a big issue. The combination of vertical
> thrust, and axial load...side thrust, and how you transfer them to the
> tower is a big issue. And how you rotate and hold a big antenna system
> is a big issue. Ignoring any part of the system is a mistake.
Yes, please don't ignore any of them.
73, Steve K7LXC
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