THE WIRELESS WORLD

Otago Daily Times, Issue 22355, 31 August 1934, Page 2

THE WIRELESS WORLD

NEWS AND NOTES

By Maoka Vox.

Items of local interest are invited by “ Magna Vox ” for publication in this column. It is necessary that such matter should reach this office by Tuesday of each week for insertion on the following Friday. 2BL, Sydney.—B3s K.C., 353 metres. 2FC, Sydney.—663 K.C., 422 metres. BAH, Melbourne.—62o K.C.. 492 metres 3LO. Melbourne.—B3o K.C., 371 metres. 6CL, Adelaide.—73o K.C., 395 metres. 4QG, Brisbane.—76o K.C., 385 metres. IYA, Auckland.—6so K.C., 461.3 metres. 2YA,' Wellington.—s7o K.C., 626 metres. 3YA, Christchurch.—72o K.C., 410.4 metres. 4YA Dunedin.—79o K.C.. 370.5 metres, 4YO. Dunedin.—ll4o K.C., 261 metres. ANSWERS TO CORRESPONDENTS. “ Battery,” Ngapara.—ln commercial forms of the cell, the copper oxide electrode is situated betAveen two zinc electrodes. The oxide is compressed, and its outer surface is reduced to form a very thin layer of copper, which provides a conducting medium. It is necessary to cover the electrolyte with a mineral oil to preA’ent evaporation and absorption of atmospheric carbon dioxide. There is no necessity to incorporate any other material with the oxide. “Amateur,” Waianakarua.—From the particulars you gi\ r e, I should say that your battery is not big enough for the set. On a large set such as yours, a change to ‘a new and smaller-capacity high-tension battery may giA-e satisfactory results for a night or two and then cause bad distortion due to serious drop in voltage caused by overload. Always use the biggest capacity you can afford; otherwise you are alAvays liable to get distortion. “ Hiss,” Warepa.—You have sent me no particulars of your set, and your trouble is therefore somewhat difficult to diagnose. Your earth may have become disconnected. in Avhich case the efficiency of the set will be decreased, making it necessary to increase the amplification. This may cause the hiss. In a super-het., the oscillator vah-e may have become soft, causing a rise in anode current. With a new high tension battery, too high a voltage may be applied to the first detector. This might cause the valve to oscillate, end so set up hissing noises. AIR-TO-GROUND RECEPTION. A Torquay wireless listener, Mr D. E. St. Ledger Grimes, reports that he recently picked up on his broadcasting receiver at home a Ayireloss telephone messagfe from a transmitter of the Obey Air Service "Dragon” aircraft, G-ACPY, Avhen the machine Avas in the air over Campbeltown (Argyllshire), a distance of 360 miles. The Olley aircraft is fitted with a Marconi type A.D.6M combined transmitting and receiving aircraft set, while Mr St. Ledger Grimes’s receiver is a battery-operated five-valve (two screen grid) instrument. He reported that conditions at the time of reception were normal, with some atmospherics, and he received the message, Avbicfi was of routine character, easily on his loud speaker. Every word was clear and easily distinguishable. CHOOSING A SET. In choosing a set, the three main factors to.be watched in arriving at a decisiem are quality, selectivity, and sensitivity. Of these, undoubtedly quality is the most important, for the majority of listeners are most concerned with Avhat they receive than the manner of the rendition. But Avith all that, there must be sufficient of the other two to ensure that the desired signals are received Ayithout any interference from other stations, and with a maximum _ signal strength. Primary factors of quality together with the necessary degree of selectivity and sensitivity should never be forgotten. If the receiver has a pleasing tone, and will bring in the desired stations without interference, then there are the ground* for satisfaction. No matter what technical features may be given to appeal, the radio has to be listened to, and this factor determines the enjoyment obtained from the broadcast programmes._ And receiver design is subject to fashion. Ncav circuits, components, methods of control, etc., may be boomed to an extent unwarranted by the technical adA-antagee, thus establishing another, fashion. Manufacturers incorporate this feature. Usually this is quite successful; although sometimes there is such little success that the new production is no improvement—in fact, often worse—on the model that has gone before it. Yet the instrument sells because of the fashion. Present trends are for superheterodyne models, which can be obtained in many forms from the four-valve set up to a type using two or three times that number of valves. Considering all circumstances, the smaller variety is capable of A’ery good results. It has good selectivity together with moderate, sensitivity, and "a quality Avhich is pleasing in spite of the fact that the output generally is limited. Five, six, and seven-valve types are sufficiently sensitive to pick up any worth-while station, and will separate them without any trouble. They also alloAv many of the refinements which .go to improve the quality of reproduction and the case of operation. The largest types combine quality, selectivity, and sensitivity to a maximum degree and can be called the “Rolls Royce” in radio receivers. Some mention must be made of details in design placed before the layman that often bring about decision in the purchase of a certain type of receive!. The advantages and disadvantages are generally obvious; but volume control should be carefully investigated—it must haA-e a smooth and wide range of control over the local stations. Visual tuning, silent spot tuning, etc., all liaA-e their clear cut advantages. Finally, when contemplating the purchase of a manufactured article, before a decision is reached a demonstration should be arranged for in the home. This will give the actual working conditions, and so the results to be expected. Undoubtedly there are some very fine sets available, and by carefully considering the A T arioiis points mentioned, the neAvcomer into radio will certainly find an immense amount of enjoyment from a tour of the ether. Superheterodynes give much more selcctiA-ity than the straight tuned radio frequency types of circuit that previously Avcre so popular. It has this greater sensitivity by reason of the principle upon which' it operates. But there is more chance of loss of quality than in the other type of circuit, and therein lies the difference between a good receiA'er and a poor one. Experience with this type of circuit, however, together with careful design and manufacturing methods, has reniOA-e_d the difficulties formerly associated with the superheterodyne—the modern receiA'er built by a manufacturer of repute meets all demands.

AN EFFICIENT EARTH. A good many readers have asked me to describe a first-rate earth connection. There arc many ways of making an earth, but probably the best of all is one that I have used with a good deal of success. It consists of a sheet of copper about I-m wide by 3ft long, and buried vertically in the ground, right under the aerial wires if possible. Don't jump to the conclusion that because you want three square teet of sheet copper this sort of earth is going to be an expensive one. There is not the least need to buy the burnished kind ot copper that is used for a chassis and so on. Go round to a metal dealer and purchase your sheet copper in the rough. You will then find that it won t run to very much. It is very cheap. # Many earth connections become faulty in tune because the earth wire is soldered to them. If yon think for a moment you will see that in somewhat acid soil this is simply asking for trouble. /ion have a copper earth plate to which is fixed an earth wire, probably of phosphor bronze, bv means of solder, which is itself an alloy of several metals. Place dissimilar metals in contact in an acid medium and everything is ready for electrolytic action. I well remember digging up some years ago a biscuit tin earth-contact of which nothing remained but the wire forming the beading round tbe rim! The earth lead for this ideal contact consists of a piece of copper tape fixed to the .Plate by means of rivets. Rivets of suitable size can be purchased from any tool-shop, and rivetting is a very simple business. In the meantime, if you are burning to get the ideal earth connection into use, either try your prentice hand at rivetting or ask the man from whom you purchased the copper to do it for you. AN OBTRUSIVE STATION. Many complaints have been made in England regarding the long wave employed bv the French station Eiffel Tower. This station works on a frequency of 207 k.c.. which is only 7 k.c. removed from the new wave of Haven try

—ISOO metres or 200 k.c. It is .indeed astonishing that after the change in control in France, the French. postal administration still permits interference with the English programmes. The publication L’Antenne at Paris is greatly perturbed about these conditions, and expresses the hope that the wavelength of the Eiffel Toiver Avill be changed speedily, so as not to interfere with the British stations. The condition among the long- j wave stations is unsatisfactory, which is •; caused by the fact that several countries have refused to sip the agreement of the i Lucerne Convention. On the medium waves the conditions are very much improved, and promise to groAv better. All stations haA-e held themselves exactly to ; their assigned wave-lengths, with exception of the French, Spanish, and Italian. Many of these stations, however, are changing their waA-es to agree Avith the international regulations, and heterodyne Avhistles are gradually disappearing. HERE AND THERE. The attitude of the national stations towards the B stations in Australia has undergone a marked change in recent j years. This dates from the time the Aus- ] tralian company had to_ go on its knees , to a B station for cricket news from { England four years . ago. Now the national service is sharing the cost of the cable messages with two B syndicates, and artists who appear before the mike at B stations can still secure engagements on the national circuit. # V * Our constructional programme seems small compared with the grandiose schemes contemplated in France. An idea of Frances broadcasting ambitions is furnished by the Post Office demand to Parliament for new credits. The 65,000,000 francs voted by Parliament in 1931 haA-e been allocated to the purchase of Radio Paris and the construction of seven transmitters, namely: Villejust, Paris, ISOkAV.; Tramoyes, Lyons, lOOkw.; Antibes. Cote d’Azur, 60kw.; Realtor, Marseilles, lOOkw. r Muret, Toulouse, 120 kw.; Thouries, Rennes, 120 kw.; and Camphin, Lille, 60 Lav. The “second instalment” is required for the Paris " Radio House,” studios ia the provinces, and many power increases.

Present political troubles bo far have prevented the carrying out of the scheme for the reorganisation of the entire Spanish broadcasting _ system. In the meantime the authorities have granted licences to some 52 privately-owned transmitters, most of which do not exceed 100 Avatts in power, permitting them to work on wavelengths of 200 and 201.1 metres. In addition to the better known Madrid and Barcelona transmitters, Oviedo (EAJI9) and Barcelona (EAJIS) hare been resurrected on 293.5 metres. The broadcasts from the smaller transmitters arc mostly limited to programmes _ of gramophone records, short news bulletins, and local talent, but it is thought that

their installation OA-er the entire country will giA-e an impetus to radio when eventually the Government scheme is carried out. * « v

Three new stations will start operations in Norway this spring. They will be located at Trondhiem and Bergen and Vardo in accordance with the Lucerne AvaA’e allocation agreement. Stations at Trondhiem and Bergen will have a power of 20kAV., while "Vardo will have only lOkw. • * * ♦

The postal administration for Berlin has given orders for the construction of a neAv ultra-short wave transmitter. This will make possible transmission of the sound to accompany the present television programmes. Both stations work on a Avavelength of approximately 7 metres. The detail of the transmitted pictures is to be increased from 90 to 180 lines. The number of frames per second remains the same —25 frames per second.