[TowerTalk] Guy wire resonance

[KI7WX@aol.com]

I think everyone that has stacking dreams must go through exactly the same spreadsheet excercise on guying materials. I know I did. A couple notes on what I did and learned.  Nothing new, just felt like adding to the QRM....

0) Yes, we all have budgets.  However, look at the tower as a system and determine where your overall costs are.  N3RR did a great job of this and presents his thoughts nicely on his web site.  Check it out.  Guy lines are a large percentage of the cost, but they are also critical to do correctly.  Most everyone will agree that antennas are the #1 priority for a ham station. The tower keeps your #1 priority in the air so why skimp on it's construction? If you are stacking antennas down the tower you've already committed to a large structure with significant costs.  Steel conducts, Philly and Polygon rod do not.  Again, you're spending a good deal of money and time on a complex system - consider present and future plans and be wary of false economies.  As a complete aside, it helps to have an XYL who says things like: "Just use 55G because I don't want to hear you whine about how 25G sucks to climb."

1) Forget about using clamps instead of grips.  I used clamps on my 45 foot tower (to save a few pennies) and will never ever use them again.  Some things in life are worth a little more money and preforms are one of them.  They are probably easier for the average dude to install properly which would make them safer as well. Not to say clamps are not safe if installed properly.

2) 55G rocks, but note that the 100 foot 55g tower cited with two guys at 50/100 feet is built to the 70 mph spec.  Take it up to 90mph Rohn spec and you need three guy lines.  We're also talking about stacking antennas down the tower - those antennas will put twisting moments into the tower in ways that the Rohn specs don't account for, and that the typical ham probably doesn't understand (I know I don't).  Simply saying two guys is OK and going forward may not be the best approach. Hank and Kurt can comment more if they like.  

Having said that, my largest tower is 105 feet of 55G guyed with Philly 6700i.  Is that overkill?  Perhaps, but I got a good deal on the sections, and rather than trying to save 10% of my costs it was a lot more important to me to build a robust structure that would be sufficient, safe, and which would meet my predicted needs for the future. 

Take home for me was simple: Towers in the 100 foot and higher range are large investments meant to last a long time. Consider them as long term investments where the costs are spread over a long period of time and then make today's judgements with this in mind. 

Happy building and do it safely!

Mark

KI7WX  (Station in /4, Operator in /6)
http://pvrcnc.org/station/ki7wx/



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