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Old 17-Nov-2015, 2:00 PM   #1
kach22i
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Antenna Mast Stabilization - Guy Wires V's Rods

I'm about to go though my first winter with a 10 foot pole, which replaced a 5 foot pole.

The five foot pole was short so there was less sway in the wind.

Come spring I may elect to shore up the mast with a guy wire system consisting of vinyl coated cable and turnbuckles for tensioning.

http://www.cableandwireshop.com/adju...enna_mast.html


http://www.cableandwireshop.com/turn...enna_mast.html


My question is, why are not stiff steel rods used in lieu of cables?

Cables are good only in tension, but rods would offer some compression strength when it comes to pushing and pulling in the wind.

There would be an increased danger of the rods fracturing/exploding under extreme conditions, but I suspect they would bend far before that would happen.

Wires don't get bent out of shape, but rods do?

Could that be the reason?

Perhaps there is a 3D loading reason which escapes me.

I'm coming from the perspective that in the lower cord of a truss, rods are favored over cables. This is because in theory the lower cord is only in pure tension, but in reality/practice there is a tiny bit of compression which must be addressed.




http://atimber.com/truss-ceiling-systems/


http://www.vermonttimberworks.com/ou...steel-tie-rod/



I may sketch up the two systems and post them, the devil may be in the details and the hardware available off the shelf.

EDIT:

It struck me that a tripod mounting is essentially similar to rigid tie rods in a fixed position.

And like this:
http://www.amazon.com/Channel-Master.../dp/B000BSKOXE

Last edited by kach22i; 17-Nov-2015 at 4:39 PM.
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Old 18-Nov-2015, 7:20 AM   #2
Stereocraig
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The main consideration, is probably cost.
Otherwise, the mast would certainly give way, well before the allthread would.

You will probably have a difficult time finding LH thread for the turnbuckle, though.
If you plan on using one, you'll probably need to ream one end out, so it's "freewheeling" w/ locked nuts on one end.
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Old 18-Nov-2015, 1:04 PM   #3
kach22i
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I have a tool for turning the end of any steel rod into a thread one, an oil is used with it.

I have the steel rods too, was going to make a rack for hanging reference drawings on (24" x 36" sets), but gave up the office overhead to work out of the home years ago - no room for it now.

The fittings at either end as you pointed out could be a challenge to source or to custom fabricate. A nice little project, if I have the time.
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Old 18-Nov-2015, 8:14 PM   #4
No static at all
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I would think wires will let the antenna system "breathe" better than a rod would allow. The mast still needs to move slightly in the wind.
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Old 19-Nov-2015, 8:26 AM   #5
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Quote:
Originally Posted by No static at all View Post
I would think wires will let the antenna system "breathe" better than a rod would allow. The mast still needs to move slightly in the wind.
I'm curious.
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Old 19-Nov-2015, 10:40 AM   #6
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Simply put, you should never overtighten guy wires to the point where there is absolutely no movement. This has been my understanding & what I have always done. Turnbuckles made it super easy to dial in the right amount of tension.
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Old 19-Nov-2015, 11:56 AM   #7
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That sounds to be more of a consideration of the wires themselves and their tendency to contract w/ temperature.
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Old 19-Nov-2015, 1:21 PM   #8
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I would assume that solid rods are more dense and rigid than cables, and hence would expand and contact more.

We are venturing into material fatigue and connection fatigue due to stress caused by thermal expansion and contraction.

The larger forces of sway by the wind are no less important, unrealistic to try to get to 100% rigid, even a masonry chimney stack must sway some.

Hinged connections are less prone to failure than fixed or rigid connections, the whole where you want what is long behind me in the structural classes I took over 30 years ago. Now I just hire a structural engineer when I need anything that critical.

This isn't that critical, but would hate to crack my mast unnecessarily.

Last edited by kach22i; 19-Nov-2015 at 1:24 PM.
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Old 19-Nov-2015, 4:00 PM   #9
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Either way will work. It is often a matter of economics and the required equipment loads and wind loads on the structure. A large self supporting A shaped tower would be an example of support by "stiff steel rods" with a wide base reaching up to support a narrow top. It has forces acting in two major directions. A slim antenna tower supported by guy cables also has a wide base (the guy anchor bolts) and forces acting in two major directions (the tower itself is one and the guys are the other). Personally I have always found it very easy and inexpensive to just add three guys to a mast such as described. I use black dacron UV resistant rope as the guy material in many cases.
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