Practical_Antenna_Handbook_0071639586

C h a p t e r 2 8 : S u p p o r t s f o r W i r e s a n d V e r t i c a l s 643
In theory, a pulley is the best way to change the direction of a support line’s path,
but few users are willing to pay for the right pulley for the task. The wrong device will
tend to rust if made of ferrous metal, or crack if made of plastic. Equally important, the
size of the pulley and the diameter of the cordage running through it must be correctly
matched to avoid jams. The smaller the diameter of the pulley sheave, the shorter the life
of the rope that lies in its groove. When selecting a pulley, make sure the groove is neither
too wide nor too narrow for the size of line to be run through it. All in all, a pulley
is not always the best solution if you have neither the time nor the inclination to select
and pay for the right one.
Figure 28.14 shows a “poor man’s” pulley, suitable for temporary installations or
lightweight (i.e., higher-Âfrequency) dipoles. In this approach, a U-Âbolt is fastened to the
top of the support mast. If the U-Âbolt is made of brass or galvanized steel, all the better,
for it will not corrode. (In general, automobile muffler U-Âbolts and inexpensive plated
U-Âbolts sold at the local hardware store will rust almost immediately; do not use them!)
The rope can be passed through the U-Âbolt as in the pulley system but without fear of
jamming. Be sure to install the U-Âbolt all the way up to the threads so that the rope has
no chance to chafe against them.
The method shown in Fig. 28.15 can only be loved by equestrians! A brass stirrup
replaces the U-Âbolt. If you have switched to cars or trucks and no longer need your
Figure 28.14 U-Âbolt end mounting.