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.
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 moist earth.
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
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.
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 are grounded.
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
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 system.
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.
Where this 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
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.
and 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