Practical_Antenna_Handbook_0071639586

664 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
tower and antenna at the top are analogous to the taut strings, and the building corresponds
to the sounding board! Now throw in the banging of any cables loosely tied to
the side of the tower and the clanging of the brake mechanism in some popular antenna
rotators. Nonetheless, the author has had a bracketed 40-Â or 50-Âft tower attached to four
different residences (often outside a bedroom, no less!) for the past 40 years. Others
have reported success in partially damping the vibrations with rubber shims between
the tower and the brackets. (A discarded inner tube is an excellent source of rubber
stock for this application.)
Often overlooked is the need for strength in the structure the bracket is attached to.
Most residential exterior walls are designed primarily to support lots of weight directly
above; they have relatively little resistance to horizontal forces. In general, a wall should
be reinforced specifically to withstand the sideward force of high winds on a bracketed
tower and antenna installation. Obviously this is most easily (and cost-Âeffectively) done
at the time the house is constructed! Under no circumstances should you expect attachment
to an existing eave or soffit to be adequate; you might as well attach the house
bracket to a raincloud. This is another area where expert help is particularly important.
Foldover Towers
A sketch of a foldover tower is shown in Fig. 29.4. This type of tower uses the same
triangular lattice construction as the fixed, guyed model but is hinged at a point between
one-Âthird and two-Âthirds the total height. The tower must be guyed at the hinge
level, and, to avoid interference with the counterbalance boom that goes up in the air as
Wire
rope
Winch
Figure 29.4 Foldover tower.