Topband: Antennas, Guy Ropes, and High Winds

[George Taft]

The Boys in Battle Creek have had good success with Dacron rope.  It
seems to have  minimum stretch and appears quite UV resistant.  We got
ours from Synthetic Textiles, I think (W0CD bought it for the group).

My 5 X 80 M verticals are all held in place by either 1/8" or 5/32"
material and have been in place for 5 years now.  I've tensioned them
every couple of years.  W0CD has been using Dacron for 15 years now w/o
a failure - essentially the same size ropes.

Little more expensive but worth the extra strength, I think.

73  George  W8UVZ


Eric Scace K3NA wrote:
> 
>    Polyester and many other types of rope are quite stretchy -- and some loose weaves are horrible in this regard.  With the long
> lengths involved, it is quite easy for the combination of sag in the guy plus stretch to allow considerable change in the
> coordinates of the guy attachment point.  This can put the vertical out of column.  Once far enough out of column, it will crumple
> over.  No guy needs to break for this kind of failure.  Changing the size of the polyester rope will not fix the problem -- it will
> make it worse because the heavier rope will sag more.  The lighter twine looks "straighter" because it doesn't have the same weight
> sag.
> 
>    Amarid and kevlar fiber ropes are the least stretchy, but also expensive.  These are used quite a bit in sailboat racing, where
> stretchy ropes are usually undesirable (one wants to keep a sail exactly in position against varying wind loads).  Naked versions of
> these lines are readily available, but check their UV resistance.  You may be better off with a covered version.  If you do not want
> to use metallic guys or fiberglass rod, then use these lines.  This will improve, but not eliminate, the issue of stretch and sag.
> Rope guying can not be used at some point, regardless of rope technology, because it will just stretch too much compared to metallic
> alternatives.
> 
>    Most of the give in metallic guys comes from taking up the slack in the guy.  For structures of typical amateur radio heights,
> the stack is small enough not to cause a relatively large cross-section tower to move far enough to come out of column.
> Thin-diameter poles are less forgiving: (a) the guys can not be tensioned as high because of the downward load placed on the
> vertical tubing; (b) a small displacement caused by taking up the sag is a much larger % of the column diameter for a piece of
> tubing compared to a piece of tower section.
> 
>    These lines will not address your initial failure mode: the break in the steel wire.  You should also take a close look to see
> why that break occurred.  Was it really a tumbleweed?  Or was the tumbleweed merely the proximate cause, and that the steel wire was
> weakened by fatigue or construction technique?
> 
> -- Eric K3NA
> 
> -----Original Message-----
> From: topband-bounces at contesting.com
> [mailto:topband-bounces at contesting.com]On Behalf Of Larry Molitor
> Sent: 2004 March 6 11:23
> To: topband at contesting.com
> Subject: Topband: Antennas, Guy Ropes, and High Winds
> 
> We had a "last winter storm" blow through here yesterday that destroyed my 90 foot irrigation tube vertical. Very frustrating, the
> thing made it all through the winter snow and ice when I was only able to operate from the cold shop building. Now, 5 days after
> moving into the new house with a nice warm and cozy hamshack, the stupid antenna falls over.
> 
> Anyway, the real reason for this post is to discuss materials used for guying this type of structure.
> 
> This 90' tube was guyed at four levels with four guys at each level. The lower three levels used double braided polyester rope from
> Syntehetic Textiles, Inc. The top level was also my top load consisting of four 17 gauge steel fence wires with 650 pound baling
> twine down to the anchor points. The baling twine is dirt cheap and so I used it temporarily while I optimized the top load
> structure. I intended to replace it with the polyester rope after tune-up was completed, however it turned out that the twine was
> the strongest component in the guy system.
> 
> The actual failure was one of the steel wires. It broke near the point where the twine was attached. I believe several things
> contributed to this failure. This polyester rope has more stetch than any nylon rope I've ever used. I was constantly adjusting each
> guy to keep the vertical straight. The twine did not stretch at all. Thus, in high winds, more of the side load was transfered to
> the top guy. In this case, additional wind load caused by a tumbleweed flying 40 feet off the ground at 60+ MPH impacting the third
> level guy was too much for the wire. After the top wire broke, the aluminum tube just folded over about two feet below the second
> level guy point at 42 feet.
> 
> All guy ropes are intact. If it wasn't for the stretch of the polyester, I think the antenna would have survived even these extreme
> conditions. Now the question is how to fix the problem. In the past I guyed permanent structures like this with steel wire of one
> sort or another and insulators at intervals. For temporary structures I always used hardware store nylon rope. Never had a problem
> with either of these methods.
> 
> Steel wire and insulators are not useable for this antenna because of the method of raising and lowering which would cause kinks and
> tangles in the wires. Baling twine is cheap and very strong, but I would have to replace it at least once a year. Since it takes
> almost two days of work to re-string the guys, I'd rather not do this. I suppose I could use a larger size of polyester rope, but
> even the smaller size I used cost more than the aluminum tubing for the entire antenna did! What to do?
> 
> Comments, suggestions, and/or discussions are invited.
> 
> 73,
> 
> Larry - W7IUV
> 
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