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Under construction
What does the ground
on or under an
antenna do?
1.) Provides
something for the
antenna to push
against. In other
words, a ground supplies the
“other terminal” for the feedpoint of
Marconi-style or
single-wire end fed antennas
2.) Provides an
alternative path for
currents that would
normally be induced
in lossy soil or
objects under the
antenna
3.) Provides a
low loss return path
for displacement
currents caused by
the antenna’s
electric field
4.) Provides lightning protection
Lightning
and RF Grounds at my Towers
Permanently grounded
towers like Rohn
65G.
Each
leg of the tower
base is grounded to
the ground system
that consists of at
least thirty
100-150 foot long #16
buried bare solid-copper wires. These wires are shallow buried.
Additionally, this tower has eight radials, fifty to one hundred
foot long, of #6 AWG solid-copper wires. The heavy wires are about 1-foot deep.
I connect copper flashing to my ground rods, which are really 1″
copper pipe, by using a step-drill to make a 1″ hole. I drive the pipe through
the flashing hole, and fill the dimpled area with solder.
Solder is “hard”
silver solder, not
plumbing type
silver solder. It takes a
MAP gas torch to
melt real silver
solder. The copper
almost gets red hot
when soldering.
Silver solder is
available from
McMaster-Carr or
from welding supply
houses.
Insulated Towers
3/4-inch copper pipe
at all three corners
of the base plate
serve as a lightning
gap on my insulated
base Rohn 45g tower.
This tower has ~100 two-hundred foot long buried radials of #16
bare solid copper wire. The radials serve as RF and primary lightning grounds.
The
arrows point to
burned marks where
lighting has caused
arcs across the gap.
I
bend the pipe in or
out to change the
gap.
The AWG 6 gauge radial buss is brazed to the copper pipes.
The
ground buss of this
tower has one
hundred 200-ft long
radials attached.
The radials are #16
AWG solid tinned
copper buss wire.
Ball
Gap Lightning Gap
My
300-ft tall Rohn 55G
has a ball gap at
the base.
This
is the much
preferred commercial method.
These are very expensive commercial static drain chokes for AM
BC towers. They are approximately 18 inches long.
Contrary to myths and false claims, static drain chokes do NOT
reduce chances of lightning strikes. They also do not divert significant charge
or protect equipment from strike damage, or nearby strike damage.
Static drain chokes accomplish ONLY one
thing.
Static drain chokes prevent electric fields from trickle
charging a tower that has no resistive or DC path to earth. For example, my
insulated 300-foot tower will charge to several thousand volts when brisk
breezes flow, especially before storms. Walking up to the tower and touching it,
on a day with a brisk breeze, produces quite a “wake-up shock”.
I’ve measured up to 5 mA of base current while the tower is
charging without severe local storms, and nearly 100 mA when clouds are low and
weather very threatening, but typically current is far down in microamperes.
Even 100k ohms leak resistance will hold the tower base down to a few volts or
less, except when lightning flashes. During lightning storms, base chokes have
virtually no effect at all on surge currents or surge voltages. They absolutely
do NOT reduce damage from distant strikes or closer strikes. They simply act as
a trickle drain to prevent a tower without any earth leak-resistance path from
climbing.
A tower fed through a series capacitor can charge the series
capacitor to several thousand volts. When the capacitor arcs, it can damage
things downstream. Static drain chokes prevent this type of damage.
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