EFFICIENT AERIALS

Hawke's Bay Tribune, Volume XXIII, Issue 74, 9 March 1933, Page 11

EFFICIENT AERIALS

POINTS FOR BEGINNERS. In view of the large number of queries regarding aerials which are received by the writer, the following hints may prove helpful to beginners who are anxious to have this important part of the set as efficient as possible (writes "Magna Vox" in the "Otago Daily Times”). First of all, having chosen the site of the aerial and obtained a suitable pole, wire, and pulleys, spare a moment’s consideration to the question of insulation. Signals broadcast from the transmitting station cause electric currehts to flow in the aerial circuit. Well, it is not going to help you much if these currents, which are extremely feeble at the best, are to be allowed to leak away. So purchase some good quality aerial insulators—glazed porcelain ones are the best—two for each end of your aerial, and thus confine all the signal energy to its proper path, which is down the wire leading to your receiver. Then make sure that the lead-down wire is efficient. If | possible this should be a continuation I of the aerial wire; that is to say, the wire should not be cut and joined up. If a joint must be made it should be a long, twisted connection, all the wire strands being well scraped, and the joint finally soldered. The ideal method would be to bring the aerial lead right into the house to the set without a join, but in most eases this is impossible, so a lead-in tube is used to pass through the window frame. Use a good one, and see that- the screwedup connections both inside and outside the house are secure. Remember that quite a lot of leakage can be caused by rain collected on the aerial running down the lead-in, and shorting to earth - at the lead-in tube. There are special types of lead-in insulators designed to avoid this source of loss, but a perfectly effective dodge is to make a loop in the down lead or even attach a small picc c of wire to it just above the leadin tube. Water running down the aerial wire will branch off at the loop and drip away clear of the tube. Keep the lead down well away from the wall of the house. This applies as much to loft aerials with external down leads as to ordinary outside aerials. Special metal brackets with insulators at the outer end can be obtained for this purpose. They are called "stand-off” insulators, and the use of these devices greatly adds to the efficiency of the aerial. The currents flowing in the aerial circuit are of high frequency, and it is a property of such currents that they can be dissipated through the small condenser formed by the aerial down lead and the walls of the house. Now, a word about the wire connecting the lead-in tube to your set. This should be as short and direct as possible, and kept well away from the wall. Also it should not run side by side with the earth connection. I saw a horrible example the other day, in which both aerial and earth leads entered the house through one small hole bored in the widow frame, and were bunched side by side for a distance of four or five feet before they reached the set. Signal- strength was poor, and tuning was "flat.” When, on my advice, the two wires were separated, and a proper lead-in tube provided, the volume increased by 50 per cent., and the selectivity of the receiver was considerably improved. If you intend to Tun an indoor aerial round your room, spend a little time in tracing the route of any electric light wires which may be embedded in the walls, and keep the aerial away from them. Otherwise you may be troubled with humming noises in your speaker due to energy picked up from the wiring. If the routes of the electric wiring are not easily discoverable, erect your aerial temporarily and listen for hum. If bad hum is obtained, move the aerial about until you find a place where the interference is eliminated. Closely associaated with the aerial is the earth connection. It cannot bo too strongly emphasised that the ideal earth is a large metal plate buried in damp soil a few feet from the house wall and connected to the receiver by a stout copper wire well soldered to the earth plate. As an alternative to a plate, a copper or iron earth tube, of which many excellent brands are on the market, will give efficient service. Some of these provide facilities for soldering the earth wire, while others have a screw terminal. Either type is satisfactory if carefully fixed. If a proper earth plate or tube is impracticable, as frequently happens in flats, a soldered connection to a main water pipe or a similar connection made by a screw clip is the next best thing. Connection should never be made to a hot water pipe, because the materials, such as red lead, hemp, and so forth, used in jointing such pipes often insulate the pipes almost perfectly from earth. It sometimes happens that no direct earth connection is possible. In such cases what is known as a " counterpoise earth” should be arranged. This consists of a wire stretched below the aerial, but well insulated from earth. It should be as well insulated as tho aerial itself. In the ease 0. a room aerial, the. counterpoise may consist or wires run under the carpet, and following a similar route to the aerial. Such an "earth” is usually quite as good as an ordinary earth, and certainly better than a poor one. AN IDEAL EARTH ROD. We hav e had bad earths which consisted of pointed metal rods suitable for j driving into the ground, and in addil tion to this the old question of the dryi ness of the soil surrounding the "earth” has from time to time received I attention from manufacturers. Tho I simplest way, of cbursOj is to pour a I bucket of water occasionally around the i earth connection in the ground, and I leave this to soak in. There are some I "earths” which consist of a hollow : I tube perforated at the sides, and adopt- , ! ed to allow water poured down the tub( . j to percolate into the surrounding I ground. All this goes a long way to-

ward improving the efficiency of the earth connection, but after all what is wanted is some sort of earth which will automatically retain really good grbund contact without the heed for periodical watering. After all, it is bad enough to have to water the flowers from time to time without having to remember to water the wireless "earth" as well. Just recently an ingenious type of special so-called "chemical earth” has bees (introduced, which depends upon the action of a substance which will, as it were, attract moisture, a«id so keep itself more or less indefinitely in good electrical contact with the ground.