AERIALS AND EARTHS

Evening Star, Issue 23657, 17 August 1940, Page 4

AERIALS AND EARTHS

DO NOT NEGLECT THEM AS IMPORTANT AS ANYTHING ELSE Aerials and earths .form two of the most important parts of any receiver, but are in many cases neglected, while in other cases are exaggerated. Any resistance in either the aerial or the earth means a reduction in the power of the received signal. The resistance of the aerial compared to the 'earth is so small that for ordinary purposes it is not worried about. The nature of the soil around the different localities varies a great deal. In one locality the ground may be sandy, which, if dry, offers a high resistance fo electrical currents, while in other places may be moist clay, which offers a low resistance. If a large area is contacted a low resistance can usually bo obtained. Unfortunately this will not always work, as a largo area of dry sand would be useless. To increase the conductivity of tho earth many salts, such as common table salt, when placed around the point of earthing greatly increase its efficiency. Many excellent earths have been constructed by placing large plates in a pit and surrounding them with a mixture of coke and salt. This is a very cumbersome method for the town, where in some places not much room is available.

A simple type of earth which is as good as any other can be constructed by placing a pipe 3ft long and about an inch in diameter in ground which has been impregnated with salts. A good plan to keep the ground “ salty ” is to block one end of it to prevent mud from entering, and drill several holes about a foot from the bottom. The pipe is then filled with a mixture of salt and water and allowed to seep into the ground via the holes. Water pipes, especially in the city, do not make the best of earths, as they are frequently used to earth much electrical wiring, which does not help clear reception. The earth wire is best placed as close,: to the set as it is possible. Again; wo find aerials that are all out of proportion to the use that they will be put. Somehow these weird and fantastic masses of wire attract wireless signals and amplify them. To-day there is not so much attention paid to aerials as there was formerly, because better sets have been constructed that can amplify the small signals that are picked up on odd pieces of wire. Despite the better sets the outdoor aerial is still the best.

For ordinary reception there is much, to be gained from the simple single wire. The higher it is above man-made static, the longer the top surface, and the further away it is from sheltering buildings the better the reception. From the above it will seem that a long, high aerial would give the best results, but there is a limit to the length, because, when it is longer than the wave length that is most used, there are noises and other problems, and, besides, in the town most people have not room for such an aerial. Pome manufacturers state a length at which their set will work best. This simplifies the builder’s task The ideal aerial would be a vertical wire placed as near to the set as possible. A wire, the highest point 70ft or 80ft, would make an ideal aerial. The total length of the aerial is taken from the point Where it enters the r t to the other end of the wire.

Not so long ago it was not an uncommon thing to see an aerial with about a dozen insulators strung along the wire. To-day this is totally unnecessary, as one good-quality insulator at each end is just as efficient. A porcelain or ebonite lead-in tube is quite sufficient to lead the wire through the wall into a house.

It is always advisable to have a lightning arrestor in the wiring to prevent blowing the valves if lightning strikes the aerial. When placing the arrestor in position make sure that it is away from moisture or spiders. Spiders’ webs, which make good conductors of electricity, can spoil all the effects of the insulation.