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Chimney Mounts
Chimney Mounts (Figure 4-7) are used more frequent-
ly than other types of mounts, but they often are not
the best option. Although they are relatively easy to
install, the smoke and gases from a chimney can
shorten the life of the antenna and significantly
impair its performance.
A chimney installation is practical only if the chimney
is sturdy and vertical. Never mount an antenna on a
deteriorated chimney. During moderate too high
winds an unguyed mast taller than 10 feet can exert
enough leverage to break off an unstable chimney.
If you choose a chimney mount, use enough mast to
place the antenna above most of the smoke and
gases. However, to avoid overstressing the chimney,
do not mount the antenna more than 10 feet above
the top of the chimney. If the height of the antenna
must exceed 10 feet to receive satisfactory signals,
the mast must be properly guyed. (The correct method
of installing guy wires is described in Chapter 7.)
Fig. 4-7. A typical chimney mount and related hardware.
Securing the chimney-mounted antenna and minimiz-
ing the stress on the chimney requires the mounting
straps to be properly spaced. The top strap should be
placed as high up on the chimney as possible. If the
chimney has a crown or projecting cap, place the top
strap directly under it. The bottom strap should be
placed 4 feet below the top strap. If the chimney isn't
long enough to permit this, place the bottom strap as
far down on the chimney as possible. If the mast must
be 10 feet above the chimney top, don't use a chim-
ney mount unless you can space the straps at least 30
inches apart. For masts less than 10 feet above the
chimney top, the straps should be spaced no less
than 24 inches apart.
Be sure the straps are level, with no kinks or twists.
The easiest way to level straps is to line them up
along the nearest course of bricks. Straps should be
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EQUIREMENTS
centered on the bricks – not over the mortar joint.
Pull each strap tight, line it up so that it is level, and
then tighten it just enough to hold it in place.
Before the straps are tightened completely, fasten
the mast to the mounting bracket. (It is assumed that
the antenna has already been clamped securely
to the mast, and one end of the transmission line
has been connected to the antenna terminals.) Align
the mast so that it is vertical. Then completely
tighten the mounting straps. Next, orient the antenna.
Finally, tighten the clamps that hold the mast to the
mounting. Be sure the clamps are tight enough to
prevent the mast from being rotated by the wind load
on the antenna.
Roof Mounts
There are two basic types of roof mounts: a base
mount (Figure 4-8) and a tripod (Figure 4-9).
Tripods are stronger and more rigid than base
mounts, but they are also more expensive. When
given a choice, use a tripod.
Fig. 4-8. A base-type roof mount and related hardware.
Fig. 4-9. A tripod roof mount.
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