<snip>
> In a message dated 2/4/04 12:06:56 PM Pacific Standard Time,
wk6f@pacbell.net
> writes:
>
> > I've seen a few postings arguing the good/bad points of torque arms.
> > For a 25G, would the torque arms be an advantage, or would the regular
> > guy brackets with six guys be better for torque control. I'm just
> > getting back into this stuff after 30 years or so, and quite a bit has
> > changed. Comments, please.
>
> Yes, changed indeed. The traditional torque arms - those foot-long
pieces
> of steel bars at the tower end of the guy wires - have been used by hams
for
> years. Intuitively they should add some torsion resistance but when Rohn
> updated their designs and calculations to conform to a new TIA-222 Tower
Standard
> revision back in the late 80's or so, they found that the torque arms
weren't
> really doing anything except when the tower was being climbed. That's when
they
> introduced the guy assemblies with the oval rings and discontinued the bar
> versions. Well, hams had apolplexy - "I've used them for 30 years and I've
got
> to have them!" - so Rohn began manufacturing them again.
>
> Are they worth using? Probably couldn't hurt. Your call. With properly
> tensioned guys, there isn't much actual twisting tower movement when the
tower
> is climbed regardless of the guy hardware so it's pretty marginal. OTOH
most
> hams don't know what their guy tension is - almost certainly too loose -
so it
> stands to reason that the torque arms might help in that kind of scenario.
I think you will find that proper torque arm performance is degraded by guys
that are not tight enough.
>
> Since the current specs call for the guy assembly with oval rings,
follow
> the LXC Prime Directive and use what the manufacturer specifies.
>
> The six-way guy brackets - the Torque Arm Stabilizer Assembly (TA25)
or
> star bracket - are quite excellent for locking down the tower since they
don't
> allow any twisting movement of the tower - it all comes down the guys. I
don't
I have them on my 45 G with the big array and find although they may help
they are do allow some twisting moment. Unless we are talking about
something different.
Mine has a three piece bracket that fits around the tower. The torque arms
fit into this bracket and are hinged to allow some up and down adjustment.
Even when clamped tight, they allow some flexing and those hinge bolts have
to be *tight*. They didn't give a torque value, but on that size bolt I
think I ran 100#. I only used torque arms at the top. I would guess the
whole assembly weighs 30 to 40#. Maybe a tad more.
I have two thrust bearings, one rotor plate, and a whole set of buy anchor
bands and rings with associated nuts, bolts, and locking nuts left over.
(and one coil of 1/4 inch steel cable left over)
I use Philistrand (tm) guy line (Kevlar). The top tier uses 6600# test line
tentioned to approximately 600# while the middle and bottom use 4400# test,
tentioned to 440#. At that tension and the light weight of the lines the
catenary curve is so small as to be almost undetectable. It is certainly
un-noticeable.
However as the Philistrand has about as much give as the High Strength steel
lines, but no catenary so they do not absorb shock well. OTOH you don't have
to worry much about low frequency resonances and tower shaking.
> know why you'd need a star bracket for 25G; if your antenna is that big,
25G
> probably isn't big enough anyway.
>
There are other dangers as well.
IF the array is large enough to require, or give the impression it needs
torque arms, what size guys are being used and to what tension? It is very
easy to exceed the tower ratings just by using larger guys and poperly
tensioning them.
By my rough calculations in my installation the top tier alone exerts over
1000# of downward pressure on the tower. with the center and bottom only
exerting an additional 400# total. (rough calcs) However if I used those
guys on a 25G the specs call for the same tension. I'd have to go to
smaller guys and use less tension.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com
> Cheers,
> Steve K7LXC
> TOWER TECH -
> Professional tower services for commercial and amateur
> 888-833-3104
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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