RADIO AERIALS

Wairarapa Times-Age, 2 September 1938, Page 7

RADIO AERIALS

NEED FOR GOOD INSULATION. Although with present-day sets the aerial does not play so important a part as it did in the days of the oldfashioned receiver, it is safe to say the reception of quite a number of receivers is spoiled because of bad aerial construction. The first essential (writes “Spark Gap” in the August “Australian Journal”) is insulation). Everything, as far as the aerial is concerned, must be sacrificed to perfect insulation. If the aerial and the lead-in are not perfectly insulated, sa that there is a minimum leakage in both wet and dry weather, long-distance reception is practically impossible. Height and length are the next two factors to be considered, and which of the two is the more important is a debatable point. In country districts, away from any powerful broadcasting station, an aerial as long as 100 feet may be used, but in the city, adjacent to most of the broadcasters, 40 to 50 feet should be ample. Forty feet is a good average height. Most aerials will fall into two classes. The inverted “L” type, which is made by slinging a length of wire between two masts and bringing one end to the instruments, is the more efficient. The other type, the “T” aerial, is very similar to the inverted “L” type, except that connection is made to the middle of the wire, making two equal lengths on either side. A “T” aerial has a wave-length of half that of an inverted “L” aerial of the same length. Except over cleared spaces, the “T” aerial is the more difficult to construct, but the best results are obtainable from it. Such is the nature of the “T” aerial that, unless the lead-in is taken from a point less than three per cent on either side of the electrical centre, only the major section of aerial will be effective. Over cleared ground, with a horizontal, insulated wire, the electrical and mechanical centres are almost at the same point. If part of the aerial is over a house or trees, however, the electrical and mechanical centres will probably be very far apart. This is the reason why many otherwise perfect “T” aerials do not give good results. The difficulty of determining accurately the position of the electrical centres renders it almost useless to erect a “T* aerial unless it is over cleared space. The vertical aerial may consist of a length of copper or brass tubing, or it may be a simple length of wire suspended from a high point, connection being made to the lower end: