Rohn 20G Verses 25G Tower

[shortride]

How many of you are using Rohn 20G towers for your directional beam antennas? Please share with me which beams you have, the weight of the antenna, how tall and how you have your tower mounted and guyed.

Everything I've read states that a 20G Rohn tower is that it's lighter duty than a 25G and should only be bracketed to a structure and a 25G can be guy-wired. I'm just wondering how many of you are getting by with guying a 20G tower.

 

[N5TWB]

A co-worker was using a 20G for a Cushcraft HF tri-bander at about 40' and the July NE OK windstorm (70-80mph) got it by pulling guy wire anchor points out of the ground. I was there the next day to observe the damage - the bottom section took the set and bent just above the joint.

 

[LtDoc]

I've had sections of both. The only difference I could see was that the Rohn 20 had one less 'Z' brace per section than the '25. That will naturally make it a little less 'strong' than the '25 but I can't say how much (take Rohn's advice).
- 'Doc

 

[n5ims]

I've had sections of both. The only difference I could see was that the Rohn 20 had one less 'Z' brace per section than the '25. That will naturally make it a little less 'strong' than the '25 but I can't say how much (take Rohn's advice).
- 'Doc

Not only are there fewer braces, but they're also smaller diameter in the 20 than in the 25. The tubing that makes up the tower sections are also of thinner material so the 20G is quite a bit weaker that the 25G although at a quick glance they both appear to be quite similar. The spec on the 20G about no guy wires is due to the thinner materials that it is constructed of will not properly withstand the stresses placed on the tower where they guys are attached.

The 20G was designed to support a fairly small TV antenna while the 25G was designed for larger types of antennas. I believe that the 20G has a 2 sq ft wind load max, while the 25G max load (which varies based on height and guy configuration) is generally many times this. Most tri-band HF beams (even the fairly light low power Jr. versions) are well above the 2 sq ft wind load so the 20G would not be recommended. The 20G is just over 30 lbs per 10' section while the 25G is almost 40 lbs per 10' section to demonstrate the difference in the material strength used to construct the two types of tower sections.

 

[shortride]

I know that a 20G will mate up with a 25G. I just don't know the load capacity of the Rohn 20G. So much for that Idea. Thanks for the input guys.