reaching heights of 90 feet or more. They can be used
for portable installations, again requiring a sturdy trailer
or vehicle. They are also expensive. Crank-ups are not
intended to be guyed, relying on the base to keep them
upright. The larger models have motorized lifting winches.
Accessories for guyed lattice towers can typically
be used on the crank-up versions. Tubular steel crank-up
towers are available for permanent installation, as well.
Bases and Guys
Even a simple mast needs a proper base to keep from
sinking into the ground or damaging a roof. (Creating leaks
or other damage to a roof is not a way to make friends
with a building manager or spouse!) The maker of the mast
or tower will offer accessories and fixtures for doing the
job correctly. They are not as expensive as having to make
repairs!
For a trailer- or vehicle-mount support, be sure the
frame is adequately rated for the weight. You may also
need outriggers or stabilizers to keep the assembly from
tipping over. Be sure to check the height restrictions for
street and highway travel as well. You won’t be driving
with the tower extended but if you are close to the limit,
be sure your antennas and accessories aren’t too high.
Overhanging branches and low wires are something you’ll
quickly learn to watch out for and avoid.
For fixed ground-mounted towers, most bases will
be concrete. Tower manufacturers will provide complete
engineering drawings for them in their literature. Bases
for guyed towers are generally pretty modest, only being
required to support the weight of the tower and hold the
bottom section steady. Check with a builder or architect
before putting a tower on top of a structure to determine
where and how to locate the tower.
Self-supporting towers depend on the weight of the
extensive base to keep the center of gravity low. The sides
of the base pressing on the soil also resist overturning
forces from the wind. If you can’t dig a hole precisely
as required, an engineer can redesign the base for you.
Pay attention to the wind-load rating of the tower, that
presented by the antennas, and stay within spec.
You should also learn a bit about concrete. Each mix
has a strength rating given in pounds
per square inch or PSI. Your base
will need to have a minimum PSI
rating that you can order from the
local ready-mix plant or mix yourself
using bags of concrete — if you follow
instructions. Concrete also needs to
set for a minimum of a few days before
you can start installing the tower on
top of it. Patience!
For guying your tower, the usual
material is 1/4 inch or 3/16 inch EHS
PRACTICAL TECHNOLOGY FROM THE HAM WORLD
Power Lines – Stay Clear!
Those warning stickers on masts and towers aren’t kidding. Electrocutions
while putting up antennas are distressingly common. The usual accident occurs
when a mast is being “walked up” and is either raised directly into power lines or
the workers lose control and it falls into them.
When siting or raising an antenna, it’s a good idea to keep your working area
away from power lines by at least half of the mast-plus-antenna’s height. Look
carefully for power lines, particularly around trees where you might not be able to
see them clearly.
n FIGURE 1 - A properly prepared climber with a fall-arrest
harness, gloves, safety glasses, and hardhat. Note the waist
D-rings for attaching a positioning lanyard. The harness
includes a seat strap and leg loops along with suspenders
and the chest D-ring for a shock-absorbing lanyard. (Photo
courtesy of Don Daso K4ZA and the American Radio Relay
League.)
20 May/June 2018
