August 1959 Popular Electronics
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Ground is ground the world around. That's a saying
that I used to hear Ham radio operators say. In a general sense, it's true, but on a local level grounds
can vary widely from location to location, even within a few hundred feet. It is true both for direct
current and low frequencies and for frequencies in to the GHz regions. It has to do with the conductivity
of the soil and/or rock in the area as well as the amount of moisture and other elements in the ground.
This article from the August 1959 edition of Popular Electronics is a good primer on the subject.
After Class: Ground, Grounds, and Grounded
By Saunder Harris
Why is a good ground so important? Why are some circuits grounded and others not grounded? What is
the physical and electrical meaning of the ground symbol when it appears in a diagram?
Grounding actually means making an electrical connection between a piece of equipment or circuit
and the earth, thus bringing the connected point to the earth's neutral potential. There are many ways
of accomplishing this. The most common way is by connecting the equipment to a cold water pipe by means
of a wire and a metal grounding clamp.
Why specifically a cold water pipe? Well, a cold
water pipe goes directly to the outside water line which is buried in the earth. A hot water pipe is
connected to a furnace or hot water heater and is not a direct ground connection.
Another way of making a ground connection is by connecting the equipment to a metal rod which has
been driven deep into the earth. The metal rod is called a ground rod and, to be effective, should go
at least eight feet into the ground. A properly installed ground rod is shown in Fig. 1.
Fig. 1. Ground rod system of grounding is good if the rod is driven well into some
If you check your TV antenna, you may find that a ground rod is part of the installation, as is a
lightning arrestor. Should lightning strike the antenna, it would find an easier path through the lightning
arrestor to the ground rod, and thus into the earth, than through your house.
A Good Ground.
Whether or not a ground is "good" is determined by the amount of
ohmic resistance between the ground rod, or other means of grounding used, and the earth. The less this
"earth resistance," the better the ground. The actual resistance measurement is made with an instrument
called a megohmmeter which applies a high voltage to a resistance and then measures the current flow.
There are many factors that determine the earth resistance. Some of the more important are:
1. Moisture content of the soil surrounding the grounding element.
2. Composition of the
soil. For example: clay is a good contact, rock a poor one.
3. Temperature of the soil.
4. Size, shape, and number of the grounding elements buried in the earth. The more element area in contact
with the soil, the better the ground. Circuit Grounds.
The ground in an electrical
circuit is the circuit's electrical reference point. Normally when something is "above" ground, it is
positive, since the negative side of the circuit is usually grounded. There are times, however, when
the positive side is grounded, as in some of the new 12-volt automobile electrical systems. In such
cases, the potentials would be considered negative or below ground. Before installing mobile equipment
in a car, it is important to determine whether the positive or the negative terminals of the battery
When a circuit is grounded and the circuit diagram shows various parts to be at
ground potential by the ground symbol, it means, in effect, that these parts are electrically connected.
This is generally done by using the chassis as a common grounding point and then connecting the chassis
to an external ground.
Equipment is grounded as a safety measure as well as for proper
operation of the circuit. If a ground connection is made to the chassis, possibility of shock through
contact with the chassis is eliminated since both you and the chassis are at "ground potential."
There are some circuits, in which the chassis is "hot," that should never be grounded. A common
example of equipment which should not be grounded is the typical a.c.-d.c. table radio. The instructions
which come with these sets generally state, "Caution: Do not connect a ground wire to this set." Since
you may have either ground potential or 117 volts a.c. on the chassis (depending on which way you insert
the a.c. plug into the power line), these inoffensive-appearing little sets should be handled with due
respect, and never be operated outside of their insulated cabinets without taking proper precautions.
Grounds and Antennas.
An antenna is nothing more than a conductor whose
specific job is to radiate or receive electromagnetic energy. Very often in ham radio the same antenna
serves for both transmitting and receiving through the use of a switching arrangement. In this discussion
we shall limit ourselves to the role that the earth, or ground, plays in the functioning of the antenna
Although antennas are sometimes discussed without taking the earth into consideration,
we cannot ignore the earth. When the antenna radiates electromagnetic energy, the earth acts as a reflector
for energy which is directed in a downward direction. These waves are reflected back by the earth and
combine with the waves which have been radiated directly from the antenna.
If the reflected
wave and the direct wave are in phase, that is, if their maximums and minimums coincide, they tend to
strengthen each other. If they are out of phase, or do not coincide, the reflected wave weakens the
direct wave to the point where, if the two waves are 180° out of phase, cancellation occurs. The way
the two waves combine depends to a large extent on the relationship of the antenna to the ground beneath
it. Is the ground a good conductor or a poor conductor? Is it rocky? Is it wet or dry? Is the antenna
high above the earth? All of these factors are important.
Currents are induced in the
earth by that portion of the radiated wave which travels along the ground and is known as the ground
wave. Valuable energy is dissipated into the earth by the ground wave and every attempt is made to keep
ground-wave losses to a minimum. Fewest losses occur when the wave travels over ground which is a good
conductor. This is the reason many commercial stations place their antenna systems near water or marsh
lands, the water or wet earth being a much better conductor than dry earth.
physical placement is not possible, in order to make the ground around the antenna as conductive as
possible, metal rods or mesh screens are buried near the surface of the earth. They extend about one-half
wavelength to either side or radially around the antenna. The actual height of the antenna then becomes
its height above this ground screen.
Many times it is practical to mount a vertical antenna on the roof of a building at an inconvenient
distance from a good grounding point. A ground system is still for the antenna to operate properly and
may be accomplished by simulating a ground condition at the base of the antenna through the use of a
ground plane system (see Fig. 2).
Fig. 2. Ground plane system is useful when an antenna must be installed at a distance
from an external ground.
In the ground plane system, copper wires cut to quarter wavelengths of the frequencies to which the
antenna is tuned are attached radially, with wires of the same length opposite each other, to the base
of the antenna mounting. They are insulated from the antenna's driven element and the roof but connected
to a good earth ground and the transmission line shield.
In effect, the ground plane system provides a ground cut to specified wavelengths and then suspended
in mid-air at the point where it is needed. In practice, ground plane radials generally act as supports
for the vertical antenna mast as well as being part of the electrical installation.
Efficiency. A sound knowledge of basic ground theory and procedures is necessary for each person who
works or experiments with electronic devices. Good grounding techniques assure the operation of electronic
equipment at maximum efficiency and with minimum electrical shock hazard.
Posted January 23, 2012