[TowerTalk] TowerTalk Rohn loading

[john at kk9a.com]

The manufacture only gives a windload specification for the top of the tower so using your Prime Directive I guess you cannot side mount an antenna in the middle of the tower. The original poster has an 80' Rohn 45 tower. I really doubt that changing a lower guy from 3/16 to 1/4 is going to cause any damaging stress to the tower legs. Rohn 45 can be stacked up to 300' high, certainly that would put more stress on the tower legs and an 80' tower with one guy wire having 200# more tension.  Adding star guys would add even more downward leg force and it is a standard Rohn product. NR5M uses them all over the place.  I use 5/16 steel and the equivalent in Phillystran for the lower guy on my Rohn 65 tower to help support the 60' boom antenna.  The tower moves less than when I had 1/4 guys and I have no worries about the legs crushing.

John KK9A


 ----- Original Message -----  
  From: K7LXC at aol.com 
  To: towertalk at contesting.com ; john at kk9a.com 
  Sent: Monday, December 10, 2012 21:16
  Subject: Re: TowerTalk Rohn loading


  >    Rohn assumes that you have other
  wind loading such as multiple runs of Heliax running up each tower leg.
  Personally I use a larger lower guy cable than specified when stacking
  antennas.

      Umm, I'd say this is a violation of the LXC Prime Directive to :DO what the manufacturer says" and the inverse which is "DON'T do what they don't tell you."

      The capacity of a tower is due to the leg strength. With a guyed tower, there is a bunch of leg pre-load due to guy wire tensioning, and don't forget the weight of the guy wires. Using larger guy wire can increase the load on the legs before anything is installed on the tower either by added guy tension or added guy wire weight. I wouldn't recommend either. 

      And use of a larger guy wire doesn't really do anything to increase the capacity or reliability of the tower. It's already been designed for a certain set of materials and parameters. 

      Violation of the LXC Prime Directive is at your own risk. 

  Cheers,
  Steve    K7LXC
  TOWER TECH