Practical_Antenna_Handbook_0071639586

676 P a r t V I I I : M e c h a n i c a l C o n s t r u c t i o n a n d I n s t a l l a t i o n T e c h n i q u e s
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Figure 29.10 Proper tower installation using gin
pole.
In use, the gin pole is clamped near the
Gin pole
top of the highest installed section so that it
can be used to raise the next section into
place. The ground crew hoists each new section
up and holds it in position while the installer
(who is belted to the tower just below
the top of the old section) maneuvers the
bottom of the new section directly over the
top of the previous one. Together the installer
and the ground crew collaborate to
gently lower the upper section onto the
lower one so that the corresponding legs of
each can be bolted together. The installer
then carries the gin pole to the top of the
newly installed section and attaches it near
the top of this newest section. If this corresponds
to a guy station, the ground crew uses
the gin pole to supply the installer with a
guy wire bracket that has the upper end of
three guy wires already attached to it. Following
installation and tensioning of the
three (or four) guy wires, the next section of
tower is raised, and the process repeated.
Guy wires are typically installed at 30-Â, 35-Â,
or 40-Âft intervals, depending on the strength
of the tower sections chosen; with Rohn 25
and 45 or equivalent tower sections, it is
appropriate to consider adding temporary
guy wires when two sections have been
added above the highest existing permanent
guy station. Some installers are comfortable
with three unsupported sections, but it depends
on your own personal “pucker factor” and whether the wind is blowing that day.
The gin pole method is preferred by tower manufacturers and is the method recommended
by most of them. For towers constructed from 10-Âft sections, installation can be
efficiently accomplished with two people—one on the tower and one on the ground.
Towers with 20-Âft sections and larger should be installed only by professionals.
The third approach to erecting towers is to rent a cherry picker, crane, or helicopter
and use it to pick up the entire tower or a major segment of it and hold it in position
while it is bolted to the base or segment below it, and guy wires are attached and secured.
This should be done only if the crew has at least one person experienced in the
proper use and stabilization of the hoisting machine. Many times, cherry pickers can be
rented quite reasonably from local equipment rental stores. They are most effective for
erecting towers of 80 ft or less. Naturally, your tower site must provide solid and safe
access for any machines you plan to bring in.