Hi Everyone,
This year, our Field Day group put up two Rohn 25G towers. Towers were erected
in the middle of a full size football field and separated by enough distance
that if either one fell, it would not contact the other. Our stations were
located about 200' from the towers to provide an extra measure of safety.
My concern that I'd like to discuss is less about the tower and antennas and
more about safety. While I hope the towers don't come down, my sole focus is
making sure no one gets hurt/killed.
Tower No. 1:
40' with 15' of mast sticking out the top with a 135' all band doublet hung
from it. Tower base was a Rohn BPH25G bolted to an 8' automotive ramp made of
angle iron (weighed about 150lbs.). Tower was pulled vertical with a truck
mounted crane with truck sitting on the 8' automotive ramp and temporary guys
made of nylon rope were attached and terminated in 2" pipe hammered into the
ground at 120 degrees around the tower. Once guys were fixed, truck with crane
was backed off the automotive ramp and headed for tower no. 2
Tower No. 2:
40' and had a TA-33 tribander on it. Tower base was a Rohn BPH25G bolted to an
identical 8' automotive ramp made of angle iron (weighed about 150lbs.). Tower
was pulled vertical with a truck mounted crane and temporary guys made of
manila rope were attached and terminated in 2" pipe hammered two feet into the
ground at 120 degrees around the tower. Truck remained parked on the
automotive ramp with crane attached to rigging on tower.
We had no issues with this installation. HOWEVER, I'm thinking we
under-engineered the guy lines. My prime concern is with tower no. 1 that had
only the guys for support (the second tower had the crane attached to the
rigging the entire time). Eventhough this installation was designed to only be
up for approximately 24 hours, I wonder if we should have used more substantial
material for the guys. I'm concerned that if someone wandered into the tower
area and tripped on a rope guy, the force might provide enough "pull" to start
the tower crashing down. In addition, the guys were "hand tightened" with
unknown tension. We used a level to make sure the tower was vertical as the
crane pulled it into position and then snugged up the guys so that the tower
remained vertical as the crane was removed from the rigging.
In retrospect, I think this was a risky installation but I'm no engineer.
Should I have bought a spool of 1/4" EHS and a LOOS tensioner and installed
these for this temporary installation or am I being paranoid? I want to be
sure that the fact we had no issue doesn't give me a false sense of security.
What would be appropriate guy material for a Field Day installation such as
I've described above?
Thank you for your input & 73,
Derek Cohn
Morse Telegraph Club - Alton Chapter
Office UD, Sine DJ
Amateur Radio Station - WBØTUA
1969 Brunswick M274A5 Mechanical Mule
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