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The following are
popular false
myths....
- By grounding
feedlines and
bleeding off the
static buildup
we are helping
reduce chances of
a lightning
strike
- We can get rid
of charges with
static
dissipators, and
reduce the
chance of
lightning hits
Where is the
charge piling up and
how can we equalize
or reduce the pile?
The charge
difference is
between different
areas of clouds, and
between those clouds
and the entire earth
and anything near or
on the earth. The
real problem is the
piling up of
electrical charges
in the droplets (or
even dust particles
in bad dust storms)
collected in one
area or another of
"clouds".
If we wanted to
reduce the charge
gradient, we would
have to create a
conductive path
capable of carrying
considerable current
between the areas
with different
charges, so charges
in those areas could
equalize.
We can do that in an
airplane by
attaching wire
brushes or whiskers
on protruding parts.
As the very well
insulated airplane
travels directly
through the charged
areas, charges can
leak off and bring
the plane to the
same potential as
whatever it is
flying through. This
is much the same as
a conductive strap
on a well-insulated
motor vehicle
contacting the
surface of a road,
preventing tire
friction from
charging the vehicle
to a different
charge potential in
relationship to the
road (and earth).
Grounding an antenna
(or adding metallic
whiskers or
porcupine balls)
does nothing at all
to reduce charge
gradient. It would
be the equivalent of
a drag-strap
discharging a
vehicle to the
vehicle itself.
Unless the strap
contacts or connects
between the
differently charged
areas with path
capable of carrying
considerable charges
over time, it does
nothing at all.
The problem we face
is the small cloud
mass far away from
the very massive
earth is charging
more and more, and
it either has to
stop charging
rapidly or there
must be a direct
path that allows it
to equalize at a
higher rate than the
charge rate.
Connecting an
antenna to earth
does nothing at all,
because the antenna
is already extremely
close to earth
potential compared
to the huge
potential difference
between the cloud
and earth. As a
matter of fact,
grounding can
actually only make
the problem ever so
slightly worse. A
grounded antenna is
solidly clamped at
earth potential,
instead of being
every so slightly
closer to sky
potential like a
floating antenna
would be.
Nature eventually
takes care of all
this. When the
charge gradient
between the cloud
(the source of the
potential) and the
earth (just a big
charge sink or
reservoir) becomes
large enough, a
streamer forms and
paves the path for
full blown lightning
bolt.
There are only two
things we can do to
reduce chances of a
hit. We can lower
the antenna, or we
can make it a very
wide blunt target.
Either one will
reduce charge
gradient appearing
at one concentrated
point. This is the
same effect that
causes a wider gap
in a spark plug or a
blunt smooth tip in
a spark plug
increases voltage
breakdown. Grounding
the shell of the
plug better does NOT
help increase
voltage breakdown,
and nether does
putting sharp
whiskers on the tip!
There really is only
one thing we can do
when the lightning
hits. When lightning
hits, we can provide
a low impedance path
to a wide area of
earth that routes
current around all
things that can be
easily damaged.
Anyone who thinks a
few six-foot or
60-foot deep ground
rods can dissipate
hundreds or
thousands of amperes
at frequencies from
near dc up to radio
frequencies with
negligible impedance
better rethink the
issue. Factually it
is almost impossible
to get rid of the
current without a
huge voltage rise of
any ground system,
so what we have to
do is be sure
EVERYTHING rises
together at the same
very same rate.
That is why we need
to bond the utility
ground to the shack
entrance ground, why
guylines should be
grounded, and why a
protected area needs
to have a perimeter
ground buss circling
the protected area.
We can't make it go
away or reduce the
odds any noticeable
amount by grounding
or snake oil cures
like static
dissipators. We
can't discharge the
clouds
intentionally. We
just have to deal
with what might
happen as best we
can.
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