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TECH NOTES—GROUND RADIAL SYSTEMS
Figure 6 illustrates the
construction of a multi-band
radial which is resonant on
40, 20, 15 and 10 meters.
Good quality 300 ohm TV
ribbon lead should be used
(velocity factor is critical),
and the conductors should employ at least one strand of steel wire to support the
weight of the radial. Four such radials will be the practical equivalent of the
system shown in figure four for operation on 40 through 10 meters.
Regardless of the number of radials used in either elevated or ground level
systems, all radials should be attached to the ground connection at the antenna
feedpoint by the shortest possible leads. An elaborate radial system at ground
level, for example, cannot be used with a vertical antenna on a rooftop or on a tall
tower, for the length of the ground lead would effectively become part of the
antenna, thus detuning the system on most or all bands.
METAL TOWERS AND MASTS
If a metal mast or tower is used to support a vertical antenna all radials should be
connected to the mast or tower at the ground connection of the antenna feedline.
This is because one of the functions of a resonant radial is to detune a supporting
metal structure for antenna currents that might otherwise flow on the structure
and thus turn the vertical antenna system into a vertical long wire with unwanted
high-angle radiation.
OTHER MOUNTING SCHEMES
In cases where a resonant vertical antenna may neither be ground mounted nor
used with an elevated ground plane, operation may still be possible if connection
can be made to a large mass of metal that is directly connected or capacitively
coupled to the ground, e.g., central air conditioning systems or structural steel
frames of apartment buildings. Some amateurs have reported good results with
vertical antennas extended horizontally or semi-vertically from metal terraces
which serve as the ground connection. Alternatively, a quarterwave vertical may
be window mounted if a short ground lead to a cold water pipe or radiator can be
used. If a long lead must be used, tuned radials may be required for resonance on
one or more bands. Great care should be exercised in such installations to avoid
power lines and to keep the antenna from falling onto persons or property.
MOBILE HOME AND RV INSTALLATION
The principles of vertical antenna installations for use on mobile homes or RV's are
the same as for other installations, and they all boil down to two main
considerations. The first is that of erecting the vertical in the clearest possible
Summary of Contents for HF9V
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