Towertalkians,
Rohn offers a service (for a LOT of money) to analyze a NON-CATALOG tower.
This means there are a LOT of ways to use Rohn towers NOT shown in the
catalog. Rohn has fully engineered and calculated the few dozen or so
configurations you see in their catalog. There are literally thousands of
possible configurations not shown there. You are not resticted to using
only the examples they show. If you choose another design, just make sure
it was done by a competent PE and you should be OK.
You think nothing of taking a boom of, say, 50 feet and optimizing the
number, length, and spacing of the elements to achieve the best F/B or
forward gain. Why not do something similar with your tower?
Let's say you have 100 feet of Rohn 45 and a guy radius of 75 feet. Your
winds may reach a maximum of 95 mph from the EIA-222-E document. The
problem is to figure out the guy configuration that will give you the
maximum allowable loading at the top of the tower. You may well discover
that by using 6 sets of guys made of 1/4" EHS, you could hold 30 square
feet. It may NOT hold 30 square feet, too. That is why it must be
ENGINEERED to find out. Rohn will do it for you, but you probably can't
afford it. You won't find the example configuration I invented above in any
Rohn catalog. That does not mean it won't work. It only means Rohn has not
chosen to calculate that one and offer it to you as one of their free examples.
If I were a PE with some spare time on my hands, I would calculate a few
configurations not in the Rohn book and offer them for sale. Each time I
did a special, I would add it to my library of saleable designs. Maybe I
could sell the same design 25 times if I picked the right one!
On the other hand, knowing how cheap hams are, 5 guys would chip in on one
design and then publish it right here on towertalk. So much for trying to
make it in THAT business. No wonder Rohn charges $5000 (minimum) plus $300
per hour to review a non-catalog tower with optional loads . . .
So what is the answer? How about an easy to understand program that allows
an average guy to plug in numbers to find out if his design is safe or not.
This may not get it past the city engineers but it may give your own PE a
design that all he has to do is check and sign rather than do all the grunt
work himself. It could save you lots of money and allow you hours of
experimenting with various tower designs with loads distributed all up and
down it until you find the very best way to use your available real estate.
As far as I know, such software does not exist at this time, but then
neither did antenna modeling software for the average guy until a few years
ago . . .
Stan w7ni@teleport.com
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