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[TowerTalk] Safety of unguyed tower

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Subject: [TowerTalk] Safety of unguyed tower
From: "Doug Ronald" <>
Date: Tue, 17 Jan 2012 20:53:42 -0800
List-post: <">>
> From the verbal description, I think these are like antennas that Collins
Radio had at their Comm Central Operation in Cedar Rapids Iowa. Twin towers
with the rotor at the bottom between the towers on a trunion and an 8 -10
inch mast going up to a log periodic antenna.


I think this type of tower was originally designed in the 1950s. The
tower/antenna was designed to be erected by being assembled horizontally The
towers would be hinged to the foundation. They would be pulled up to
vertical using a winch truck pulling horizontally, over an A frame to start
the lift. The truck was placed about two tower heights from the tower base
away from the tower to keep the pull as horizontal as possible. Lift off was
the tricky part.


Once the towers were in place and guyed, the log periodic antenna was
assembled upside down with the mast on top and the rotor sitting in the
trunions. The winch line was run from the truck over the top of the tower
and down to the  top of the horizontal mast. As the mast was pulled up, the
antenna would pivot. First dropping to vertical as the top of the mast rose.
When the mast reached vertical, the top of the mast was restrained in a
bushing or bearing of some kind between the two towers. The log periodic
antenna continued to pivot around the top of the mast to get to its final
horizontal orientation.


One of the  interesting features of the assembled antenna was the fact that
the rigid 50 ohm feed line ran up the center of the mast and had a rotary
slip joint on the bottom below the rotor that permitted continuous rotation.




Yes, a correct description except for the towers being hinged at the base -
they are not, however the ground-based rotator is on a trunion which allows
the rotator to be positioned orthogonal to the towers for assembly of the
mast with later winching to vertical as you described.


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