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Fixed Wireless Equipment

The Guys You Depend On

How good are your antennas? How good are the towers they're on? Be warned—you may be depending on some guys you don't know.

[August 3, 2004]

On the ISP-Wireless list in July, JN wrote:

Well, the weather really took a hit on us. When you get a page that one of your towers are down, you don't expect to go and find that it actually fell over!

Several list members shared similar bad weather experiences.

[DL said] "All in one week, we had lightning hit and snap one of our top guy wires (actually an antenna mast guy—not the towers itself). Then, two days later, high winds bent the extension pole for an omni on our 225 ft tower. And the previous week we got a direct hit on another tower from lightning that fried our equipment and a lot of the radio station's also. All in all a good excuse to get rid of this Aironet stuff we've been meaning to take down for ages."

[KG related] "We took two direct lightning hits on the July 4th weekend. Got them replaced and took another direct hit yesterday afernoon. Been raining ever since. Maybe tomorrow."

Other list members asked for more information.

[FC asked] "What failed? Guy anchor point?"

[TI added] "Some days stink in this business. This looks like a good ad for guy wires. How many sections were you running above the house bracket without guy wires? Grid antennas have increasing wind load profile as wind speed increases. At some wind speed, they effectively become a solid instead of grid."

[BG queried] "While weather undoubtely played a part, this looks like a good argument for more and heavier guy wires (and/or protecting the anchor points). How many guy wires were there, and at what levels?"

[CB asked] "How tall was the tower above the house bracket?"

[BM asked] "How did you get the guy points 120° apart with a parking lot covering what looks like 180° of your ground space?"

JN answered some questions:

The tower ran 90' above the house bracket.

There were 6 guys, first set around 40' and the second was around 80' give or take a few on those. I think the guys could have been heavier but not sure that would of even made a difference.

If you look at the pics you will see in one a big cement yellow pole, these were placed on the parking lot end and used as guy points. On the other end they were actually guyed to anchor points on the building's steel framing. Kinda strange, but that is how the tower company did it.

TI had a vital recommendation:

One thing I see on a lot of on Rohn 25G towers is guy wires wrapped around the legs of the tower section instead of using the Rohn guy bracket assembly. The brackets definitely make the tower stronger and twist less. Also make sure that your guys are not too tight and that they come out from the tower at the recommended angle if at all possible. I think Rohn recommended approximately 30 feet between guys.

[JN replied] "You know, actually you are right. That is exactly how they installed the guys, wrapping them around the legs and not using any guy brackets!"

[TI suggested] "That is fairly common, as the brackets were around $70 each when Rohn was still in business. Many residential market tower companies give little thought to engineering and more to cutting costs. Guy wires attached directly to the legs are applying forces on the guyed tower section to pull the legs apart. This force and pull gets worse as the tower twists and the guys tighten in the wind. The bracket changes that force to a uniform downward pull. If you are replacing the tower, have your installers follow proper engineering and it will last a lot longer."

[SC added] "We have repaired so many Rohn towers that have been built improperly: poor anchors, un-galvanized guy wire, no safety wires, spliced guy wires, no guy brackets, missing grounding rods, no lightning rods, rust everywhere, etc. We just replaced a 150' rohn 25G with 3 guy levels that had 6 - 3 foot solid dishes and 2 - 2 foot dishes as well as a 10 foot omni. They were wondering why when it was stormy they lost all their links. The tower was swaying about a foot or two in any direction due to extreme overloading. This was taken down and replaced.

The 25G towers can work well if engineered properly. This is not a tower that has much compassion for shortcuts. As a rule of thumb, every tower should be inspected annually to check for rust, loose connections, missing bolts, etc. Not to mention running a transit to make sure the tower is plumb and using a Dillon to check for wire tensions. All of these things can be done preventatively to avoid the reactive situation of a fallen tower. Luckily no one was hurt :)

Good luck with the new tower! I wouldn't recommend trying to salvage anything. Just scrap it all and start over."

Finally, JM asked for all the details:

I've looked at the pics and read your posts. I still haven't figured it out. What failed? Did the guy wires break? Or did you loose an anchor point? What happened?

The story had a happy ending, as JN reported:

"Well, we have the new tower put up. What seems to have happened was the high winds snapped one or more of the guy wires which caused the chain reaction to the rest of the guys. Then you know the rest after that. I hope we have better luck with bad weather and this tower!"

RY had one final question:

"Just curious... Did you do the original installation?"

[JN replied] "No, the tower was already erected before we came into the scene."

—End