EARTHS FOR EVERYBODY

Radio Record, Volume VI, Issue 51, 30 June 1933, Page 25

EARTHS FOR EVERYBODY

In this article the importance of making a good ground contact is explained, and practical advice is given on the most popular methods of obtaining an earth connection which will ensure reliable results.

AVING concluded our "Chat About ~ Aerials" last week, we will now consider the earth, which should be just as carefully installed. In effect, the aerial and earth act as the two plates of a condenser, with the air between them as dielectric, and so to pick up the greatest amount of signal both plates should be as electrically efficient as possible. Nobody would think of using a tuning condenser with half its’ plates perfectly puilt and the other half just thrown together in a haphazard way, but this is what occurs when a receiver is connected between & firstclass aerial and a poor earth. The beginner is often confused by

the bewildering variety Ot earths he finds are employed by his friends, and so is nonplussed when trying to decide on the best. The problem is not at all complicated, however-it_ is just a matter of keeping to a few common sense fundamentals. Once the aerial has been erected there is very little choice as to the best locatan far the earth. for it

eee ie ie should always be directly underneath the aerial, as shown in diagram 1. As mentioned before, the ground below the aerial acts as a condenser plate, and 80 the nearer the earth connection is to the ground directly under the aerial, the more efficient will be the installation. What Is a Good Earth? A most important qualification of a good earth is that it must have low resistance. ‘To achieve this, the earth lead shouldbe short, of fairly heavy gauge wire, and the earth plate or rod to which it is soldered should be buried at least four to five feet down in moist ground. We will deal with these now in turn. A long earth lead is certainly not

(lesirable, because if it wanders around the room before reaching earth, it has a damping effect on the system, and in consequence tuning will be flatter. Also a long lead acts like an aerialinefficient, it is true-but it places the set "up in the air," often making it unstable. The wire employed should be of fairly heavy gauge, because the earth lead is really part of the aerial system, and there is not much advantage in choosing a heavy wire for the aerial and a thin one for the earth. Nothing smaller than number 16 s.w.g. should be employed. Perhaps the best’ wire ‘to use is stranded aerial wire, because

of its larger surface area and also because the strands can be separated and soldered to separate portions of the earth plate to ensure the best pos sible connection. Tt is not at all essential that the earth lead should be insulated. However, if it is not, and if it is at all slack. it will possibly be blown against a wet wall or nearby shrub, causing fading and scratching noises in the speaker. After all, enamelled wire

might just as well be employed, be cause it is as cheap as bare. . The last and perhaps most important provision to ensure a good low resistance earth is that the earthing de-, vice, whether plate, tube, or waterpipe, should make ample contact with moist earth. Dry earth is a poor conductor of electricity, and for this reason, the earth-plate or rod should be buried several ‘feet away from the house,. where’ the ground it.is buried in is not ‘sheltered from rain-by the. eaves. . In earth connections, as in the aerial, perfect joints are essential, and every nrecantion must be taken by soldering

or a very tight clipping (in the case of : waterpipe) to see this is the case. The Best Earths. The most common earth connection is one made toa water pipe. This’. generally forms an_ excellent earth, because these pipes run deep down under the enrforea of the wrronnd. and

a te ee, -_ el the soil around them is generally moist because of leakage from the pipes themselves. Make certain, however, that the pipe does not ramble all over the house before going to earth, and also always choose an incoming pipe from the water main, and never hot water pipes running from a cistern. Remember that regulations prevent the use of gas pipes as earths. Connections cannot be made to cold water pipes by direct soldering because the cold surface carries the heat away faster than the soldering iron can apply it. This difficulty is commonly overcome in three ways, illustrated below. In all cases the pipes should be sandpapered clean before the connection is made. (Continued overleaf.)