In a message dated 99-04-22 11:11:59 EDT, W4EF@pacbell.net writes:
> Can anyone tell me what the length is for the Rohn TB25 torque bars that go
> with the
> GA25GD guy bracket?
They're approximately 16 inches long.
> They are not shown in the catalog and I am wondering if they
> create a larger or smaller cross section than the TA25 torque arm
stabilizer
> assembly.
You mean physical size cross section? I think the TA will be larger.
>
> I am trying to rebuild a large HF stack (300 lbs/20 sqft) and am concerned
> about
> rotational inertia and wind induced torque being transmitted from the
> antennas thru
> the rotator and into the tower. I have seen some broken welds on the
current
> installation,
Something that size on 25G? Sheesh. Are you still in Brevad County,
FL? That's a 105 MPH windspeed zone. Why are you so grossly overloading your
tower with your proposed installation?
> but this appears to be due to a faulty rotator installation (the rotator
was
> attached to the
> rungs instead of the tower legs as a quick "get on for the contest" kludge
> and was never fixed).
If there was a similar load on it, I'd say that the damage was due to
severe overloading and not specifically due to where the rotator was
installed.
The *best* place to mount a rotator is at the guy points. That way,
the wind induced torque on the tower is transmitted to the guys which is much
easier on the tower system.
> Is it better to let the tower twist with the load, or stiffen the
> tower with the torque bars?
You would like to get no or minimal torque on the tower system. The
torque arms don't really contribute anything to the tower torque resistance
which is counter-intuitive. The Rohn torque arms only really contribute to
tower stability when it's being climbed. That's why Rohn re-designed the guy
assemblies to use the current oval rings and (years ago) dropped the torque
arms from their product line. Hams complained ("That's the way I've ALWAYS
done it!") and Rohn put them back in the catalog.
If you maximum torque resistance, use the TA torque arm stabilizer
which uses a double-guying system to "lock down" the tower.
>And if I install the torque bars, how close should the rotator
> mounting point be to one
> of the torque bar augmented guy points?
Well, if you want to use them they should be as close to the guy
attachments as practical.
But the basic question remains why the severe overloading?
Cheers, Steve K7LXC
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