Wireless Broadcast

Star (Christchurch), Issue 17881, 24 June 1926, Page 14

Wireless Broadcast

CONTRIBUTED BY

“AERIAL.”

BETTER AT 600 MILES THAN AT 300. Radio signals are better 600 miles from a broadcast transmitter than they are at 300 miles, according to engineers of the radio department of the General Electric Company, tinder whose supervision an exhaustive investigation of radio wave propagation is being made. For several weeks past thousands of radio listeners have been co-operating with the General Electric Company by reporting on reception of signals on broadcast bands. These co-operative tests are still under way. and the conclusions are only such as suggest themselves from the preliminary reports. The engineers do not’ claim that the conclusions are absolute and caution that more exhaustive investigation may reveal some facts not yet apparent. In observing the variation of signal strength, it was found that the strength drops off rapidly during the first 300 miles from the station, and that contrary to what might be expected, the signal strength actually increases and is apparently a little stronger at 600 miles than at 300 miles. Beyond the 600 mile point the strength decreases again slowly to the limit of the range of the station. These distances are not definite values: they are averages from a large number of reception reports. A study of the zones in which fading occurs shows that it is worst at about 200 to 500 isiles from the station, and this zone, from 200 to 500 miles, is the territory in which there is the greatest percentage of rapid fading reports. Broadcast service is better at 600 miles than 300 because - fading is less and the signal strength is slightly greater. These distances vary slightly with the power of the transmitter. Rapid fading is not often observed, however, and in this respect the regular broadcast waves seem to be different from the short waves. The reports indicate that the rate of fading increases steadily as the wavelength grows shorter. The main objective of the investigation in co-operation with widely scattered volunteer assistants is an answer to the question—what is the relation between weather and radio reception, or do weather conditions influence radio ? Variations ol signal strength, static and fading are all btigbears of the listeners. and an effort is being made to regulate Ihc.sc irregularities to changes in barometric pressure and temperatures. If definite relationships between radio reception and weather conditions can be established, it will be possible to predict receiving conditions in any part of the country as reliably as it is now possible to forecast weather conditions. Thus far investigations by the General Electric Company engineers indicate that the connection between barometric pressure and temperature with radio conditions is not definite, or if it is definite, it is so complex that it is not understood. Temperature seems to have no effect on the signals themselves, although it is known that there is an increase in static in summer. The study so far shows that the barometer makes little difference when conditions at both the transmitting and receiving ends are alike. When transmission is made from a high to a low area, transmission is best at short and long distances, but at medium distances of about 600 miles it is best from an area of low pressure to one of high pressure. The phenomena is apparently related to the distribution of storm areas over the country and requires a great deal more study. NOISES IN THE RECEIVER. DEFECTIVE PARTS ONE CAUSE. A large percentage of the trouble experienced with radio receiving sets by the average B.C.L. may be traced

directly to little things that go wrong with the movable parts of a set. The variable condenser, tube socket and rheostat are concrete examples of this statement. From the time the first radio set was built up to the present, trouble has been experienced with poor contacts in these instruments. Poor volume, noisy reception and fading signals arc frequently caused fey defects in these pieces of apparatus and not by interference from outside. By examining any one of these parts it is easy to see what is causing the trouble, and it is often as equally easy to correct the difficulty. The tube socket will be considered first. This device, in addition to being a home for the tube is used to connect the prongs of the tube to the receiving circuit, and it should perform no other electrical function. Many of them do so, however, by allowing current to leak away, these losses being due to poor insulation and dielectric losses. As most fans know, the prongs of a standard vacuum tube (American base type), are four in number and consist of brass tubes about half an inch long with a lump of soft solder at the end. The socket may be an}' one of a hundred designs, but it always has four metal conductors -which make contact with the prongs of the tube. Many sockets employ springy contacts of phosphor bronze, designed to bend upward and make contact with the tips of the prongs. Right here are two possibilities of trouble. First, the solder on the tip of the tube prong will coat the socket contact with lead oxide (a poor electrical making a high resistance connection. Secondly, the spring may lose its resiliency and fails to press against the tube hard enough to make a good contact. The first of these difficulties may be cured by cleaning the tips of the tube prongs with a small fiat file, and in the second case it is only necessary to bend the springs up a little more in order to make good contact. In the case of variable condensers there are two frequent causes of trouble —poor contact with the rotary plates, and contact between the two sets of plates due to the fact that one or more of the moving plates has become bent. To correct the first fault it is advisable to solder a flexible wire to the shaft of the condenser and connect it to the terminal connecting with the moving plates. To fix a shorted condenser is often possible by merely bending the buckled plate back into position, but sometimes this is impossible, and the best cure is a new condenser altogether. Rheostats cause trouble when the wire forming the resistance element becomes corroded, and when the contact spring loses its tension. Both these faults may be located by an examination, and are easily put right. A rheostat of the carbon compression type, however, is much more difficult, and when they begin to get noisy through wear or over-heating, a new one is necessary. It is not worth while pulling them to pieces to remedy the trouble, as their construction seldom permits of this. JOTTINGS. Quite a goodly number of local fans report reception of Australian 2KY. This is the Trades Hall broadcasting station in Sydney. Up till recently 2KY was quite low-powered, but the output is now 1500 watts, and con--sideration is' being given to provide further increased power gup to 8000 watts. A very comprehensive scheme of expansion along the lines of news service, entertainments, and education has been drawn up by Mr C. G. Christie, who has recently been appointed director of the station for a long term to enable him to carry out the plans drawn up by him.