RADIO

Southland Times, Issue 21263, 9 December 1930, Page 15

RADIO

SHORT WAVE.

DEVELOPMENT SHOWN.

(By

R. J. Orbell,

8.E.).

During the past years it has been the dream of radio enthusiasts to be able to listen to programmes from stations in all parts of the world. The ability to sit. at one’s receiver and swing the dial first to London, then Paris, then New York, and so on round tho world, has for many years presented a powerful appeal Io the imagination. This was in the early days of radio. More recently, the advent of short wave transmission, and a certain little peculiarity attached to it, has indeed made this wish come true. Experimenters discovered the fact- that when very short wave lengths are used, the signals have what, is called “skip effect," that, is to say, waves jump right over nearby receivers in their travel and come to earth again at very great, distances, thus losing practically no energy by motion along the earth's surface.

Prior to this all-important discovery engineers built stations to operate on very long waves in the belief that, their signals would travel over great distances more effectively than with medium wave-lengths as were used originally. In this assumption they were correct. It was found, however, that very high power indeed was necessary if the signals were to be heard on the other side of the world. Another serious difficulty with the use of these ultra-long waves was met with. This was that static interference which was found to be very much more troublesome than with the medium waves, sometimes rendering operation entirely impossible. Very high lattice towers were necessary and the cost of stations ran into many thousands of pounds. • Then the pendulum swung in the other direction, and strangely enough the first to make satisfactory use of ultra-short waves were amateur experimenters. They had been allotted the use of these very short waves by their respective governments who believed that, these were useless for commercial purposes. The amateurs communicated over astounding distances with extremely low- power, with barely any static interference, and at a cost, that was infinitesimal when compared with that necessary for the long waves then in use by the Governments. Naturally all attention was turned to these short waves as offering immense commercial possibilities. New Gov-ernment-owned short wave stations grew up almost over-night. Beam stations which concentrate the waves in one direction were developed and operated morse at high speed from one country to another. Experimental short wave stations were erected in various countries for the purpose of transmittir- musical programmes to other countries, and great success was met with. Two years ago, the British Broadcasting Corporation erected a station at Chelmsford about, twenty miles from London, with the express purpose of conducting experimental transmissions to the Dominions, of the normal London and Daventry programmes. Interest in these daily transmissions became world wide, and a vast field was opened for broadcast listeners in the Dominions possessing short wave receivers. Development in America was at the same time proceeding along similar lines. The high powered short wave stations of the General Electric Coy., 2XAF, 2XAD. and 3XAL were erected at Schne.ctady close to New York. Others were 9XF at Chicago, BXK at Pittsburg, 6XN at Oakland, California. These slations, now rapidly being supplemented by numerous others, continued to transmit daily programmes, the reception of which, although subject to slight fading at times, was found to be quite satisfactory in all quarters of the globe. Attention in Holland, German” and Australia was also turned to short wave broadcasting, till to-day the rapidly expanding list of stations includes several hundreds of call signs. Those possessing short wave receivers will be interested in the recent cabled announcement from London stating that,the British Broadcasting Corporation intends further to develop its services to the Dominions by the construction of a super station, capable of reaching all parts of the Empire even under adverse conditions. Following on this announcement conies another indicating that Vienna. Budapest and Warsaw are to be connected by a relay chain with London. This will mean that programmes presenting the world’s foremost Continental artists wlil be available for transmission by the new British short wave station.

The geographical position of New Zealand is ideal for reception from British and Continental stations, inasmuch as it is close Io their antipodal points. Strange as it may seem at.first sight, when we locate a receiver as far as is possible from a transmitter, that transmitter Is actually received many times more strongly than if it were closer. The reason for this is that waves travelling from a transmitter in general follow great circles on the earth’s surface. Since all great circles originating at one point meet again at another point, exactly opposite on the globe, it is not difficult to understand then, why reception is better at that point. That partly is what actually happens in actual practice, and although refractions and reflections due to the two twilight bands somewhat modify this result, nevertheless the concentration in New Zealand of European transmissions is most marked.

During a recent trip to the Antarctic on the “City of New York" of the Byrd Expedition, the writer was able to follow closely the effect, of this concentration of signals from European stations close to the Antipodes. As the ship moved further south, European stations became weaker than in New Zealand, whereas stations in the United States became .somewhat stronger. Incidentally this occasion made one realize more than ever, the incalculable value of shortwave radio, in mainfaing contact with remote places over great distances, when long wave apparatus failed to maintain contact with the closest, land, (wo way communication was carried on daily with New York, as easily as over an ordinary telephone.

Regular weekly shortwave broadcast transmissions from America to the expedite ion members in that remote locality enabled the latter to hear distinctly the voices of their friends and relations at home as well as musical entertainments provided by these stations. Although shortwave broadcasting Ls now becoming very popular with radio listeners, it will never supercede the longer waves for short, distance transmissions, on account of lhe “Skip effect” referred to above. The owner of a modern long and short wave receiver has the choice of either short and medium range programmes or long waves or extreme distance on short waves. He has either at his command and so is enabled to realize in fact, the dream of the early experimenters. The limit of his seat is the world. The ordinary broadcast set will not receive shortwave stations, but there are one or two receivers on the market specially constructed to receive shortwave as well as ordinary broadcast programmes.

TELEVISION.

CRITICISM OF PLAYS

In the course of his criticism on the first play by television, which was recently broadcast by the Baird system, the dramatic critic of the London Tinies said: “Let it be admitted at once that plays by television are as yet a subject for men of science, not for critics of the finer points of acting. The visual transmission is far from perfect. You feel yourself to be prying through a keyhole at. some swaying, dazzling exhibition of the first film ever made.” In connection with improvements in television, the critic went on to say: “How far off these improvements arc only Mr Baird and his men of science can judge. Men of the theatre may meanwhile rest in peace. The time for interest end curiosity is come, but the time for the serious criticism of television plays as [Jays is not yet."

ON THE EUROPA.

MODERN WIRELESS APPARATUS.

LONG AND SHORT-WAVE.

The new North German Lloyd liner Europa is equipped with the most, modern wireless apparatus. It permits permanent use of three lines in duplex, which means that, messages can be sent as well as received on all three lines at the same time. Ihe transmitter does not affect the receiver, although it is installed directly alongside it in the same room and the aerials are fastened lo the same masts. This duplex system is especially notable for its long wave traffic, as the transmission wave length differs, only a few per cent, from the receiving wave length. Six radio telegraphists are necessary to work this apparatus. The radio equipment which was supplied by the Tclefunkcn Company, consists of a transmitting and a receiving section, lhere is a chief transmitter operating on long waves and destined for direct communication with both continents from any point between the coasts. Its range is from 5005,000 metres, and provision is made for high-speed transmissions. An auxiliary transmiter operates on the usual wave band (580-830 metres) reserved for shipping purposes and destined for communication with coastal stations and other ships. A short-wave transmitter provides for telegraphic and telephonic communication over very great distances, with an aerial output of 700 watts and wave lengths ranging from 15 to 01 metres. Then there is an emergency transmitter as a special reserve in the case of a breakdown in the power plant of the vessel. The operation of the emergency transmitter is entirely independent of this electrical plant. The receiving section consists of a newly designed ultra-sensitive and ultra-selective receiver for wave lengths from 150-2,000 metres, with additional tuned band filter. The congestion of all wave lengths used at sea and the need of rapid handling of the wireless traffic demand receivers which by the greatest possible selectivity and sensitiveness still remain so simple lo use that the attention of the operator is occupied as little as possible by the tuning in to a desired station. In addition, the cabin is fitted with a short wave receiver for wave lengths from 10-150 metres with high frequency amplification, and an S.O.S. receiver to pick up at any time an S.O.S. or alarm signal on wave length 600. independent of all other communications. A special receiver with loud speaker is always tuned in.

The ship is fitted with direction finders, which arc an indispensable help to navigation, especially in foggy weather. Four motor-driven life boats are fitted with wireless, placed in the covered-in bows of the boats. The necessary current for these small stations (sending .wave length 600 metres) is generated by an accumulatorbattery of 24 volts and roughly 100 amp. hours. This battery can be recharged, if necessary, from the water-tight enclosed motors. The wave range of the receivers is 300-1,100 metres. The two-wire aerial is carried on two collapsible masts on board each boat.

RANDOM NOTES.

As tho input to your set depends in the first place upon the aerial, the higher this is placed the better.

So effective is the potentiometer control of grid bias in the detector of a short-wave set that it is now usually regarded as a necessary modification of such a circuit.

Generally speaking, it is. not worth, attempting to obtain grid bias from a mains unit, as the trouble is greater than that of buying n battery occasionally.

If your L.F. transformer has exposed leads to the windings remember that a break in one of these or a faulty connection will give the same symptoms as a "burn out.”

The increase in licences for the Commonwealth of Australia for the month of June totals 870, which brings the number of licences in force to 312.192. Every State with the exception of Victoria, which decreased by 1009 licences showed an appreciable increase. Following are the increases for the various States:—New South Wales, 571: Queensland, 538; South Australia, 281 ; Western Australia, 203; Tasmania, 286.

An “Omar Khayyam Phantasy’" will be presented from IYA by Mrs Zoe BartleyBaxter on August 26, when the story will be told in both words and music. The "atmosphere” of the Orient will be conveyed to listeners by street noises and appropriate sound synchronization. Mrs Baxter will also present on the same evening a “Comedy of Three Centuries," which will consist of excerpts from comedies of the 18th, 19th and 20th centuries.

The fact that over 50 charges of operating unlicensed wireless sets were dealt with in the Auckland Police Court, recently is evidence of the “radio piracy’’ being carried out in Auckland. Listeners were doubtless pleased to note that the magistrate made the punishment fit the crime by imposing heavier fines on those with unlicensed multi-valve sets. It is hoped that all offenders in this tespect will he brought lo justice. The benefits conferred by the licence fee of 30/- a year are many, and will be increased with larger numbers of licensed listeners.