Tower Time – Part 2 – Tower make and model
Based on confirmed research 100ft AGL would get the job done, so the hunt started. I looked at the online used tower sites and viewed a used 120ft Rohn SSV which was available in the KC area. I wanted a free-standing structure so the choices were a bit limited and I examined AN, Rohn and Universal. The distributor for AN did not return my queries and the Aluminum Universal is only rated for a 200lb climber so I passed on both. Which left me with two choices new Rohn or a used Rohn. I now have two short Rohn 25g towers at the house, both of which I have had since my teenage years and I am not concerned about their ability to age well.
Next factor to consider is wind loading, which all summed up is under 10 sqft given my current plans. The used SSV is rated at 10 sqft using the standards in effect when originally delivered, which from my research was Rev D. The same tower config SSV using the current Rev G standard is down rated even further to 6 sqft if memory serves. As by this time I was looking for other options as the SSV light duty line did not meet my expectations and the heavy duty line is crazy expensive both in structure and foundation cost.
To make this all more interesting I had begun to engage the county zoning department on antenna structures and learned that any structure would need a engineers stamp for the state of Missouri. Which I learned in practice is best gotten from the manufacturer as tower design is a specialty skill which requires special modeling tools. The problem is when dealing with a used tower, an inspection is required to ensure that the tower is in good condition prior to an engineer stamping the plans. Which if one has gotten the tower for free it makes economic sense, and as this was not my case the cost of the tower, inspection and stamped plans was too close to a new structure to not chose new when I was considering the Rohn SSV.
A good primer from Rohn on Rev G. Understanding Rev_G
I next looked to the Rohn RSL line (http://rohnnet.com/rohn-rsl-self-supporting-tower) and was impressed by the capacity to cost ratio and that bearing and rotor plates are available from the factory. It is available in several ANSI/TIA-222-G configs which is a need everywhere you need a building permit.
RSL Spec excerpt
The next step is getting a building permit, which requires stamped drawings so an order was placed.
Next stop the building permit process. Stay tuned…