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Ground Zero for your receiver

by Ted Benson
(as published in Frendx 5/89)

Most of us who grew up in the "nuclear ages" think of ground zero as the impact point of a nuclear warhead. To radio enthusiasts, however, it can moan something completely different.
The ideal ground for radio reception represents zero ohms of resistance, and no impedance whatsoever. As with everything else in our hobby, however, there is the theoretical, end then there is the reality. In reality, perfect ground is impossible to attain. Commercial radio stations bury thousands of feet of copper wire to obtain a good ground, and even this is not perfect. But why is a ground connection important at all?

Electricity flows only when a difference in potential exists between two points. There are two power prongs on our wall sockets (the third is a ground - more on this later). At any one time, one prong has far more electrons than the other does. If you connect a circuit between the prongs (such as a lamp) the excess electrons will flow through the circuit to the other terminal, in an attempt to reach a balance. It is the flow of these electrons which performs work - in this case lighting the lamp. Unless current flow can occur, no work can be done. Ah, you say, what about the time as a kid when you stuck a key in the wall socket? Only one prong was connected, but you still got a nasty shock. Where did the current flow to as it coursed through your body? It flowed through your feet to ground. Because the ground wasn't very good, only a little current was able to flow and you survived (literary folks - this is no joke). Many people are killed each year because the ground was good. Perhaps they were wet or standing in water, or barefooted on moist soil. The better the ground, the more work (or harm the electricity was able to do.

Your shortwave receiver is in essence a circuit, which is connected to a power source similar to your wall socket. In this case, though, the power source is the radio signal you wish to resolve. How can a potential exist when the entire signal flows through the air? The question provides its own answer! The radio energy is almost all in the air. Almost none of it is in the ground. The potential exists, therefore, between the air and the ground. But how do we plug our circuit - the receiver - into the air and ground? Well, the air connection is of course made by an antenna, which gathers as much signal as it can. The ground connection is made in any number of ways. Many people simply connect the ground terminal of their receiver to the little screw in the middle of the wall socket. Others drive a stake or rod into the ground and connect this to the radio's ground terminal. Neither of these techniques is really adequate. Although the little screw on your wall socket is a moderately good ground for 60 Hz AC, it can literally appear as an open connection at radio frequencies. In other words, relying on this point as your ground is like making no ground connection at all! Driving a copper rod into the earth might provide a good ground connection, if the soil around it was very conductive. Most soil, though, is not. Some method must be used to increase the conductivity of the soil around the ground rod. Figure 1 suggests a technique for improving the conductivity of the soil.

Figure 1. Suggested ground rod installation.

Older reference books suggest using copper or nickel chloride instead of the table salt (sodium chloride) shown in figure 1. Although the copper and nickel chloride do work better than sodium chloride, they also contaminate the soil. In this age of ground water contamination, as is rampant here in the Silicon Valley, the last thing we need is to contribute more! Table salt, as shown, is also much cheaper than other salts. In fact, a huge bag of water softener salt works fine, and can cost as little as $5.00. In areas of very dry soil, it may also be necessary to "water" your ground occasionally to keep the soil moist in and around the pit.

Why all this bother about a ground connection? Well, as we saw earlier the ground is the other half of the power source. The better a connection you make to the power source, the more signal will flow through your receiver's front end. And the more signal that flows, the more you will hear!


Now that we have a good ground, how do we connect it to our receiver? Many receivers, particularly the older ones, have a separate binding post for the ground connection - either as a ground terminal, or as one half of a balanced antenna input. Newer receivers often come with only a coaxial connector. The outer shell of this connector is ground. When using this type of receiver simply connect the ground wire to the shell of the connector. Be careful when connecting to any other metal part of a receiver - particularly tabletop models powered by the wall socket. In some of these receivers the chassis may be "hot", that is, it may have a substantial amount of AC voltage present. This voltage will arc and perhaps trip a circuit breaker when grounded. Also, many receivers do not have all of the metal chassis parts connected together, so you may be connecting to an insulated bracket instead of the receivers' front ends. Always use heavy gauge wire {#14 as is used for house wiring is good) when connecting to a ground, and keep the length as short as possible.

Exceptions to the rule

Many antennas are designed to be used without a ground. Instead of using the earth as the other half of the power source, these antennas contain two elements, and each element in effect becomes an opposite pole of the power source. Examples of these antennas are dipoles and Yagi beams. But even with these antennae, a ground can often improve reception, if for no other reason than it lowers the noise level. For the most common types of SWL antennas, like the random wire or vertical, a ground is absolutely essential.

One other aspect of the ground has not yet been discussed. Safety can be enhanced by the use of an outside ground. Most have never seen what lightning can do when it strike an antenna and enters a house while looking for ground. I have. As a Coroner, I once visited a home in which the amateur radio operator had grounded everything to the wall socket ground. Well, lightning can be very unpredictable. Before it eventually found the wall socket ground it travailed around his radio shack, and took a detour through him in the process! I implore you, if using a coaxial feedline use a lightning arrestor as well. If using a random wire or similar antenna, use a large switch as close to where your antenna lead enters the house as you can, and use it to short your antenna lead to ground when not in use. In either case, connect the arrest or switch to the outside ground. It's a little inconvenience that can save a lot of inconvenience.

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