[Table of Contents]People old and young enjoy waxing nostalgic about
and learning some of the history of early electronics. Popular Electronics was published from October 1954 through April 1985. All copyrights (if any) are hereby acknowledged.
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.
By Saunder Harris
GROUND, GROUNDS, AND GROUNDED
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.
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.
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
A Good Ground
Fig. 1. Ground rod system of grounding is good if the rod is driven well into some moist earth.
Fig. 2. Ground plane system is useful when an antenna must be installed at a distance from an external 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
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
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.
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
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).
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. Safety 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