[TowerTalk] Safety of unguyed tower

[Steven H Sawyers (na0ia)]

 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 up side 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 it's 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.

Steve