Checking guy wire tension?

[Bill, KD0HG]

How does one check the tension of guy wires?

I know the pro tower crews have some sort of gizmo that they use, but what about the rest of us?

Also: My tower is guyed with Phillystran, not steel. Would that make a difference in how tension was measured? Phillystran is a lot more limp than the customary EHS galvanized steel.

[WBear2GCR]

Hmmm... sounds like a job for strain gauge technology? 

Or, you could pluck them like a bass guitar string and measure the resonant frequency??

Although, actually, IF they are all mounted to the same length (presumably they are) you could take a spring scale of some significant weight ability (like into the hundred pound or more range, rig it to grab the guy wire at some convenient point, apply tension with a come-along or other tensioning device and then use a measuring device to measure the deflection accurately at some given poundage.

That will tell you the relative tension between the guys.

I think you can determine the actual tension through some math (that I don't know off the top of my head).

                 _-_-bear



                  _-_-bear

[k4kyv]

If you can find the formula, one method is to place some sort of rigid frame next to the cable, that touches the cable at two points a known distance apart.  Then at the midpoint between the contact points use a spring scale to displace the cable a specific measurable distance.  The tension will be proportional to the amount of force required to displace the cable.  You might find the specific formula in a textbook somewhere.

There is a gadget called a dynomometer that works on the above principle,  but does it automatically by just clamping onto the guy wire.  I have one, but don't trust it because I don't get consistent readings.  It seems to work well enough for small cables, but it is not consistent when I try to read 3/16" EHS cable.  I think mine is too small.  You  might be able to borrow one from someone who does tower work.

I did mine on my tower simply by eyeballing it.  I tightened the turnbuckles on one set until they seemed reasonably tight but not too tight, and observed the sag, then used that as a standard to go by for the rest.  The NAB Broadcast Engineer's Handbook explains how to do this in order to get consistent results for each guy level.

It is said that you are supposed to tension the guys to 10% of breaking strength, but when I tried that to the best I could measure it,  it seemed too tight to my liking, so I loosened them up just a bit.  The tower has been up for almost 30 years now, and I see no signs of wear or fraying at the attachment points, which is supposed to be the reason to keep them that tight, to minimise movement when the cable sways.

One factor to consider is temperature.  I can see a big difference in mine between hot summer weather and sub-zero winter.  I adjusted mine to be slightly loose in summer and still not too tight in the coldest weather.  Some tower people recommend readjusting according to the season, but that seems like a lot of extra work for nothing. I think the best approach would be to do a compromise, maybe by adjusting them to specs in the autumn or spring, when the temperature is about midway between normal extremes for your area.  If I did adjust mine to 10% of breaking strength, I'd try to do it on the coldest day of the year.

[John K5PRO]

A Loos tensionmeter, model PT2, is the 'recommended' way. You can find them online, often on EBAY or CRAIGSLIST, when a sailboater is selling out. I bought one from Champion Radio and used it last winter. For Phillystran, you must install a leader (a few feet is all that is needed) of 3/16 EHS at the bottom so that the PT2 can clamp onto it. It will not work with Phillystran directly. I set mine for roughly 10%, found that they vary wildly as you move around the three guys during tensioning. You can really see the effects of other guy wires being adjusted, so it is a gradual thing, like tuning and loading a final amplifier circuit.

[K1JJ]

Bill,

How have you found Phillystran to be for stretching?  Does it need to be tightened periodically about the same as EHS?  What size are you using, the 6,000 lb stuff?


I've always used steel EHS here with insulators for Rohn 45, 1/4" cable, and use homemade star guying with large torque arms (6 guys) at most levels.  But the "RF invisible" feature for higher band Yagis is quite nice with Philly.

BTW, I adjust my guy wires by look and feel. The longer, the more droop. The should whip around a little when you swing them by hand, but not too much.  I have some guy anchors that are out about 190' from the tower. Those guys have quite a bit of droop and still are probably close to 300-400 lbs of pull. I agree with Don that 1/10th (600 pounds) is too darn tight.


Though, much will depend on the load the tower holds.  Pushing a tower to its torque limits with stacked 40M or 75M rotary Yagis means closer spaced guys that are more accurately adjusted.  A tower holding a few inverted vees has a cake walk life.


Don:  Do you use guy brackets on your tower to interface with the guy cables at each level or are you connecting directly to each tower leg? Your chafing comment got me wondering.

T

[Fred k2dx]

My homebuilt 20 meter beam is guyed with Phillystran so as not to detune the elements, laterally and vertically by 8 pieces of 1/4" (I think) Phillystran maybe 25' long. Each one with a ss turnbuckle at two central spreaders. There isn't any stretching that I can see after 20 years  keeping in mind they are a short length compared to a tower guy.

The more tension on tower guys the heavier the compressive load on the tower legs. I would think without a means of accurately measuring tension it would be better to err on the lighter side. 

Self supporting towers do have several advantages!

[k4kyv]

How have you found Phillystran to be for stretching?  Does it need to be tightened periodically about the same as EHS? 

I use Phillystran between the ends of my dipole and the wooden poles some 450' away.  It is the lighter grade stuff, next to the smallest size they make (or made in the mid 80's).  I have a couple hundred pounds pull on it, and it has never seemed to stretch.  After more than 20 years, the sag over the 450' distance has not changed, and I have not had to readjust the turnbuckles.

I wouldn't run Phillystran all the way to the ground for two reasons.  One, if there were ever a grass fire, it could burn the guys in two and drop the tower.  Secondly, a vandal could easily drop the tower with a razor blade or sharp pocket knife.

BTW, I adjust my guy wires by look and feel. The longer, the more droop. The should whip around a little when you swing them by hand, but not too much.

That's basically how I did mine.

Don:  Do you use guy brackets on your tower to interface with the guy cables at each level or are you connecting directly to each tower leg? Your chafing comment got me wondering.

I use guy brackets, but without the torque arms.  I also use a thimble with each guy wire connection, so I don't think chafing would be a problem no matter how much the cables sway in the wind.  I remember reading somewhere that that's the reason for the 10% tension recommendation, because if the cable is simply wrapped round the tower leg (in proper fashion with the zig-zag braces so that the guy wire tension doesn't tend to pull the tower apart), and the guys are too loose and sway in the wind, the chafing will eventually wear off the galvanising and could lead to failure due to rust.  In reality, that seems a little far-fetched to me, but I am aware that if anything can possibly go wrong, it probably will.

BTW, I use 3/16 EHS cable and 3/16" thimbles.  I have noticed lately in the tower catalogues that they sell only 1/4" thimbles and recommend them for the 3/16" cable.  I don't know if they have quit making the 3/16" size or what, but the smaller ones work better with the 3/16" cable.  Also, I have noticed that the ones I have seen for sale recently use cheap zinc plating that will rust away in about 6 months, instead of hot-dipped galvanising.

Actually, I would much prefer the older HS cable instead of EHS, but apparently no-one made the HS cable any more, even in 1980.  It does not have quite the breaking strength of EHS, but it's a hell of a lot easier to work with.  You can wrap it tightly, and it stays tight without springing back loose like EHS does.  I almost lost an eye when I was constructing my tower, when a strand of EHS broke while I was trying to wrap it.  It hit me in the eye sideways, hard enough to leave a visible dimple on the cornea.  I found the broken piece, about 2" long, and the broken end was sharp as a needle.  I was lucky it hit me sideways and not by the sharp end.

I used a hunk of 3/16" HS on another antenna, and it was a pleasure to work with.  I notice the older Rohn catalogues from the 1960's still list it, and it was cheaper than EHS.

[Bill, KD0HG]

Hi, all, great ideas and discussion.

Tom, I'm using the 4,000# rated Phillystran, it's a bit more than 1/4" diameter. After 10 years of hurricane-force winds in the winter, it's held up well. Absolutely no, zilch, nada stretch is evident. That Kevlar *is* like steel. Even though it all looks good, I wanted to square up the tower this summer and re-tension the guys.

It is truly frightening watching that stick in 100+ MPH Chinook winds off the mountains. It doesn't budge, it doesn't twist, but the forces on it must be nasty.
 
I terminate the bottom end of each guy with turnbuckles and a 6' steel leader, just in case of a grass fire.

Don, I also dislike that EHS stuff...About as much a tangled-up wad of #12 Copperweld, LOL.

John, thanks for the tensionometer tip. I Didn't know there was such a thing.

I did call the guy that does tower work for the local radio stations..He suggested that guys can be properly tensioned pretty much by just taking out any sag by pulling as hard as you can by hand, cranking them an RCH more with the turnbuckles after that point, and calling it good. Since a properly-sized guy won't stretch, you don't need them any tighter than that. He said that you can 'feel' when they're properly tensioned. Pretty much what you guys said, and the way I installed the thing to begin with.

There isn't any sag in my guys as the Phillystran weighs a fraction of a steel cable.

Maybe it's that simple.

[k4kyv]

I have seen the newer Phillystran that is woven just like steel aircraft cable.  You can terminate the ends using u-bolt cable clamps or a special variety of guy-grip preforms, just like steel cable.  Mine is the older type with the fibres simply bundled together inside a black plastic jacket that looks like RG-58, and terminated into an epoxy-like potting material.  I remember mixing the resin and hardener, fanning out the fibres like bristles on a brush, inserting them into the end piece, pouring in the mixture and letting it sit overnight.  The plastic cable is lightweight enough that there is very little sag over the entire 450' run.  The whole 900' roll weighed only a  few pounds. As I recall, Phillystran was originally developed for marine use where the salt environment corroded steel cable, and someone thought of the idea of promoting it as a substitute for metal guy wires.  For obvious reasons, it is widely used on communications towers in coastal areas, and its rf transparency makes it good for AM broadcast antennas.

[Bill, KD0HG]

Yup, I'm using the Phillystran that uses standard preform cable grips on the ends.

I remember the stuff that you had to epoxy the end fittings on...That must have been 20 years ago. What a pain.

Another reason I went with Phillystran was that I felt that it wouldn't be prone to lightning damage. I've got no proof of my theory, but I once saw a 1/4" guy cable fried by lightning strikes.

I'm using 1/8" Kevlar twine to hold up one end of my 80M Zepp. It's about 400 feet from the end of the antenna to the utility pole end support. I tried using steel fence wire, which was too heavy so the span sagged too much. Regular rope was also too heavy and nylon twine too stretchy and not strong enough. The Kevlar twine is perfect- The span only weighs a few ounces and it easily takes at least 50# of tension.

[k4kyv]

I'm using 1/8" Kevlar twine to hold up one end of my 80M Zepp. It's about 400 feet from the end of the antenna to the utility pole end support. I tried using steel fence wire, which was too heavy so the span sagged too much. Regular rope was also too heavy and nylon twine too stretchy and not strong enough. The Kevlar twine is perfect- The span only weighs a few ounces and it easily takes at least 50# of tension.

I originally used #10 copperweld wire, broken up with strain insulators every 25 ft. or so.  It was very heavy compared to the Phillystran, but I managed to tension it enough to reduce the sag to a reasonable value.  But after a year or two I noticed that I was  losing strain insulators.  I took it down and inspected it, and turns out lightning was destroying those insulators.  Every single one had multiple cracks and some even had evidence of molten glazing and holes right through them.  Some just fell apart after being split open by lightning.  So I replaced that wire with Phillystran and never have had any more problem.  The feed point insulators are all OK.  I still have them and they have never sustained any noticeable damage.

But the same thing happened to the bottom set of guy wires on the tower.  I  had to replace all the insulators after an apparent direct hit.  None of the insulators on any of the top sets of guys were damaged.  I replaced the bad ones with some larger size insulators, and now on one of those the end has cracked and fallen off, but there is still enough left that the rest of the insulator is still mechanically and electrically sound.  I have a replacement insulator and set of guy grips set aside to do the repair, but I have been putting off doing the job for a couple of years now.

I don't know if it was lightning, someone with a rifle, or if the insulator (a used one from the power company) already had a crack that I didn't notice when I installed it.

[K6IC]

Interesting discussion ... The only important thing regarding Phillystran tower guys is that this materail is strong, resiliant (returns to original length after being stretched within reason),  and RF invisible,  but it stretches more than steel guys under the same force.

There was a very nice discussion of Phillystran vs EHS guys here,  about 9 months ago.  It regarded an artilce that K7NV had posted on his site.  The bottom line seemed to be that it was  more difficult to keep a tall tower "in column" in big winds when using Phillystran,  and that a Pier Pin base would be an important attribute for tall towers guyed with Phillystran.

Using this site's 'search' funtion,  was unable to find this thread. ... BUT here is a link to K7NV's Notebook article on behavior of Guyed Towers with various loading. :

http://k7nv.com/notebook/towerstudy/towerstudy1.html

There is a button in this article,  called "Guy Cable Link"  which may be of interest.

Am not smart enuf to figger out how to search effectively on these sites

EDIT:  Using Google,  found this link from almost two years ago :   

http://amfone.net/Amforum/index.php?action=printpage;topic=11559.0

Was started by K4KYV Don

73   Vic.

[WQ9E]

I went through this process several years ago and used the tension gauge I bought for my bandsaw.  I had to calculate the desired PSI reading of 1/4 EHS based upon tension in pounds and of course I have now misplaced my results so at some point I will have to go through that again.

If you know someone with a large wood or metal cutting bandsaw, there is a good chance they will have a tension gauge.  I bought mine the same time I bought my 24" MiniMax bandsaw and fortunately the tension gauge will fit on 1/4 EHS in addition to its intended use on bandsaw blades.

Rodger WQ9E

[K1DEU]

  A picture of my little 160 ft. 45G tower, exclusively guyed with .3 inch OD phillystran/aramid. The two upper guys are terminated with Torque arm stabilizers from Norm's fab in Michigan. The last 30 feet and beams done by Matt of http://www.xxtowers.com/

I use strand vises to terminate and tension the 1/4 inch galvanized ground porcupine leaders. Some of the leaders are 40 feet long as I enjoy small trees near the 12 foot 10 inch guying screw augers. 

The first 50 feet of tower was straightened and checked with a carpenters level. The remaining guys were tensioned by feel/insight and tower sighted up from its three sides for straight. One of my guy points is much higher than the tower base and closer.

On top is the little Comet  6, 2 & 70Cm Vertical hooked to a FT-8900R through 200 feet of LMR600.

Next down is the 6 meter Force 12 5 element beam for my Lafayette HA-460 through LMR600 .

Then a space for the two 2 meter 7 element vertically stacked beams being assembled soon & 70 Cm.

On the bottom above the Yaesu thrust bearing (laterally supporting 11 feet of 61T6 2 inch OD, 1/4 in. wall pipe) is a small trap-less Force 12 C3S/HH 140 mph survival, 6 element, 1 reflector/1driven element on each band.
Short 12 foot boom for 20, 15 & 10 awaiting the next ice storm test!  http://www.force12inc.com/

Feedlines are 1000 feet of LMR600 and 500 feet of LMR400 available UPS from Maryland on e-bay.

Before Winter I will add a 80 meter bi-square quad towards New Mexico which will be feed at the 153 foot level (upper inverted V supported by existing philly guys) At the bottom will be a vaccccummm relay to short the bottom V section, affording an 160 meter loop feed at the top. Regards  John, Southern Vermont
Click picture twice to enlarge

[W2VW]

  A picture of my little 160 ft. 45G tower

This proves that you don't spend all your time in that bathtub.

[KM1H]

Another place NOT to use Phillystran is where tree branches can break off and fall or even rub as the branches grow.

Also what has great clearance in June doesnt look so good with a snow load.

I had a 100' of 25G with a 10-15-20 stack of 4 el yagis at my old place with that early type cable and had to change one side to steel....pine trees grow fast.

Here I use 1/4" EHS steel broken up with insulators according to the old Antenna Manual graphs. The cable was free from CATV crews and is used on 4 towers from 60' of 25G thru the 180' 45G.  Nothing cracked in 20 years and Im on top of the highest hill in 20+ miles.

Carl
KM1H

[k4kyv]

Here I use 1/4" EHS steel broken up with insulators according to the old Antenna Manual graphs.

The NAB Broadcast Engineers' Handbook recommends breaking the guy wires for AM broadcast towers into lengths of 1/7 wavelength, maximum.  I wanted my tower guys to be rf  transparent through 40m, so that came out to segments of guy wire 18' long.  If I had planned to use the tower only as a 160m vertical, I could have saved a lot of money and work,  by spacing the insulators every 72'.

[nq5t]

I just stumbled on this while looking around for something else.  Scroll down to the bottom of the page.

http://www.championradio.com/rigging.html

Grant/NQ5T

[John K5PRO]

Yep, that's the one I mentioned earlier, this thread. PT2 for 3/16 EHS.

[KM1H]

The NAB Broadcast Engineers' Handbook recommends breaking the guy wires for AM broadcast towers into lengths of 1/7 wavelength, maximum.

I believe Im using 51' spacing. However from what has been reported only the first lengths from the tower and the top set of guys are critical when yagis are mounted on top. Since I ran stacks on rotatable side arms all lengths and levels were broken up. A random length went to the guy anchor and had several large ferrite beads mounted at the ends..... a trick I learned in the 80's when debugging a problem with a commercial repeater site. Corrosion in the guy anchor hardware was causing intermod. I wrote this up in a 2 way magazine as well as the Yankee Clipper Contest newsletter.

Guys are all secured with Guy Grips/Big Grips which place minimum strain on the insulators as compared to bending the wire and using clamps.

Carl
KM1H