Practical_Antenna_Handbook_0071639586

698 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
Vertical monopole
Elevated radials
Coaxial feedline
I
N
Ground buss ~
S
Earth ground
Figure 30.7 Elevated radials for a ground-Âmounted vertical.
the return currents are collected by the elevated radials, even though there may be only
a handful. “Far enough away” turns out to be l/8 or more.
Unlike radials on the ground, elevated radials exhibit resonance in the same way
that an antenna does. Thus, all radials for a given band should be cut to the same length
and should all make approximately the same angle with the ground, insofar as possible.
If the vertical (such as the 14-ÂAVQ) is capable of multiband operation, a set of l/4 radials
should be added for each band to be used. The objective is to make the impedance
at the feedpoint end of each active radial as low as possible in order to maximize the
return currents it supplies the vertical monopole. One possible simplification might be
to add traps so that a single set of four or eight radials serves multiple bands.