I know I will be pounced on by most Radio Amateurs and a good controversy may stimulate some interesting discussions! So here goes.......
It has been an axiom in radio to ground our stations to the earth. The deeper the ground rod the better . Modern theory of lightning shows that there are two parts of a lightning bolt. One is a streamer the drops out of a thunderstorm, the other is a streamer coming up from the earth. When these streamers connect, pow a lightningbolt is produced.
The cloud has a negative charge which comes down, (from a cloud ), called a step leader(s). The earth has a positive charge with respect to the leader(s), called a streamer(s), when these meet, a current flows upward and a lightning stroke is produced.
What if you were not connected to this path? Why would the lightning bolt want to travel to your antenna or rig if you are not connected to any thing that is in the lightning path ! Shocking eh! (pun intended )
Much of our practices were handed down to us by the pioneering hams and have never been challenged by us. The idea of grounding the vertical antenna is derived from the fact that if we ground one side of our transmission line to the earth, it then becomes a mirror image of our antenna or the other HALF of our antenna. Radials are often used to improve the conductivity of the Earth, or the other half of our antenna, but a connection to the earth is not what we want. What we want is the OTHER half of our antenna. When mobile, we use the body of our vehicle as the second (mirror) half of our antenna. Dipoles, beams, quads etc, type antenna's, need no ground connection at all to work just fine.
There is another consideration for grounding, and that is
Now a little bit about the damage that lightning does to appliances in a home. The damage to rigs, TVs etc. is due to the voltage surge caused by a lightning strike near the power company's ac line and when the lightning bolt's magnetic field collapses, this generates a rise in the voltage coming into your house.
I made a good living repairing the damage caused by these induced voltages coming in on the power lines. When we had a direct lightning strike we just picked up the pieces as no repairs were possible. A lightning strike contains so much energy and it is so fast that nothing can prevent the devastating damage of this energy.
The best prevention effort for surges is to install very
good, and as always, expensive, surge suppressors across the ac line where
it comes in to your home.
You should have in your shack a buss bar connecting all of your equipment together using the shortest and largest conductors as practical. This is done to prevent chassis currents between equipment and different potentials between equipment, that may occur but no connection to the EARTH is needed.
There are many examples of taller ungrounded, or poorly grounded structure not being struck and a lower nearby grounded structure i.e. a tree, a grounded antenna etc. suffering a strike. Lightning seeks the lowest resistance/ inductance grounded path.
As an example that I have personally witnessed, when a neighbor across the street had his dog chained to a wire strung between two metal clothes line posts which were in the ground and about 6ft. tall. Lightning struck a pole and his dog was almost electrocuted! Fortunately the dog lived after extensive medical treatment. What makes this interesting, is the fact that a 30 ft tall tree was only 20 feet from the clothes line and it was untouched. I believed the dog survived because the wire had a high resistance connection. The wire was loosely twisted on the poles, making a high resistance connection and the dog did not receive the full voltage.
Lightning rods, invented by Benjamin Franklin, were placed on buildings to safely conduct a lightning bolt's energy to ground. Back then, tall buildings had a poor connection to ground and installing a lightning rod supplied a low resistance path for the lightning bolt to ground. When a building was wet it was possible for a strike to hit it, resulting in the building catching fire, from the energy it was conducting to earth.
As you may know, California has many fires each year due to lightning setting trees on fire. Why isn't your home equipped with a lightning rod? I believe it is not a problem in modern times because of the way homes are now built, effectively isolating the building from the ground.
Now consider this: Your 100 ft. tower with your excellent ground, is a great lightning rod, so along comes the usual thunderstorm, the lightning bolt strikes your tower and a ga-zillion amps flow safely to earth through it. Safely? Such a huge current flowing produces a huge magnetic field, and when this field collapses a huge voltage is induced in nearby conductors, such as antennas, coax lines, rotor cables, ac lines etc., this induced voltage is what does the damage to your equipment! If the tower were not grounded, then no current flow would go through it and hence, no induced voltage hence, no damage.......now put that in your pipe and smoke it!
Ok, I threw down the gauntlet; I will now put on my hard hat and await your onslaught.
Earl Schlenk (Email w0es AT hotmail.com )
1051 Mersey Bend Dr. Apt. D
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