-15-
TECH NOTES—GROUND RADIAL SYSTEMS
MOUNTING TUBE INSTALLATION
When tube w/insulator (A) is ground mounted, it should be protected against
corrosion if placed in concrete, damp acidic or alkaline soil. Asphalt roofing
compound, polyurethane varnish or other sealant that protects against moisture
may be used.
Concrete may be used in areas of high winds for greater strength, in which case
the post may be twisted slightly during setting for easy removal later.
Tube w/insulator (A) must be installed in a hole approximately 21 in (53.3 cm)
deep so that the upper end of the fiberglass insulator is approximately 7 in (17.8
cm) above ground level. Pack earth tightly around tube w/insulator (A) so that it
remains vertical.
NOTE: HAMMERING TUBE W/INSULATOR (A) INTO THE EARTH MAY CAUSE THE
INSULATOR TO SPLINTER. If the post must be hammered into the earth, protect
the end of the insulator with a block of wood
NOTE: DO NOT USE U-BOLTS TO ATTACH TUBE W/INSULATOR (A) TO A MAST,
TOWER ETC. U-BOLTS WILL EVENTUALLY CUT INTO THE TUBING AND
WEAKEN THE INSTALLATION. If U-bolts must be used, place a larger diameter
metal, such as the MPS Mounting Post Sleeve over tube w/insulator (A). Similar
precautions should be observed when using TV style towers with locking bolts.
The RMK-II Roof Mounting Kit includes the MPS as well as the STR-II Stub Tuned
Radial Kit.
GROUND MOUNTING
A vertical antenna in its simplest form, is electrically equivalent to
one-half of a dipole antenna stood on end. When the antenna is
mounted close to the ground, the earth below takes the place of the
"missing" half of the dipole. If ground conductivity is fair to good, a
short metal stake or rod may provide a sufficiently good ground
connection for resonant and low SWR operation on the bands for
which the antenna is designed. This basic arrangement is shown in
figure 1.
The way it works is that the capacitance between the vertical radiator and the
ground causes
return
currents to flow along the earths surface back to the
transmitter. If they have to come back along untreated lossy earth thy get back
to the source greatly attenuated. This
return
loss is like a resistor in series with
the antenna radiation resistance and will therefore affect the feed point
impedance.
Summary of Contents for HF9V
Page 14: ...14 Feedline Detail PICTORIAL...
