RADIO RECORD

Greymouth Evening Star, 21 April 1938, Page 11

RADIO RECORD

NOTES FOR LISTENERS-IN

(By

“Reception”)

PUSH-BUTTON TUNING. DIFFERENT SCHEMES. Tuning the receiver by the simple process of pushing a button marked with the call sign of a station is being applied by an increasing number of manufacturers (writes N. M. Goddard, 8.E., in the “Sydney Morning Herald”). Probably by the end of the year some form or other of this type of tuning will be included in one or two models at least by every maker. For want of a better term, selection of stations by push buttons or their equivalents has been called automatic tuning, but, as these methods are solely mechanical, they should be distinguished from schemes, in which, by electrical means only, circuits have their characteristics changed to tune them exactly to the signal, and which are known as automatic frequency control.

In the application o£ the schemes now finding favour, there are many awkward electrical and mechanical problems to overcome, awkward because the cost and complication must bo kept within reasonable limits. Consider the case in which a. small motor is called upon to rotate the tuning elements of the receiver to the correct position. It must act in the same way as an automatic lift, always bringing the mechanism in the correct direction, to exactl’ r the position that is required, no more and no less. As a pure engineering undertaking, this problem supplies no insurmountable difficulties, but, us a. combined mechanical and electrical problem, there are complications, because the required positions have a tendency to move. It is as if an automatic lift has to cope with floors that were likely to move up and down in the building in a manner unknown to the lift. In any receiver there are a great number of components, which by reason of temperature changes, variations in atmospheric humidity, vibration and so on, will change their values. Therefore, before the mechanical part of an automatic station selector system can be successfully combined with a receiver, the physicist must produce ma-

terlals which will not change when temperature and humidity vary, and the radio engineer must produce circuits which are unaffected by such changs as do occur or which will automatically make allowance for such changes. It is because such materials and circuits have been produced that a degree of mechanical tolerance can be allowed in the selecting mechanism which has simplified construction, and has made such schemes economically possible.

In general these selecting systems can be divided into two classes, one in which a motor takes charge of the operation and moves condensers or other tuning elements of conventional type, and the other in which a number of combinations of suitable pro-tuned components are supplied and the various combinations are substituted one for the other or in groups as required. In both instances selector switches arranged so as to prevent conflicting and impossible conditions are also required. In the case of the motor there must be a suitable form of reversible driving unit, which in some cases may bo of tho impulse type, such as are used in automatic telephones. The method of substituting various members of pre-tuned combinations has the advantage of relative cheapness and also the instantaneous appearance of the wanted station, but it requires considerable electrical stability in the circuit and skilful initial setting. The motor-driven schemes have a powerful appeal in the idea of u motor-driven gear and switching system actually replacing the hand of tho owner and performing automatically the mechanical business of tuning. Some of them have the further great advantage of lending themselves fairly easily to means of true remote control. No push-button selector scheme will, of itself, improve any of the usual characteristics of a receiver, except in so far as they make it compulsory that most of the circuit components shall be of first-class quality. They will certainly reduce tuning to what has been described as a lazy man’s task, in that they will take from the operator the labour of manipulating the controls, and also the necessity of exercising judgment as to the correct final tuning position. This last point may be of considerable advantage to unskilled or careless operators, because failure to tune correctly can spoil the quality of a programme, and in spite of indicators and such things, there are still many who fail to perform the tuning properly. This, of course, presupposes proper electrical and mechanical design and construction. Faults in these respects would possibly create a state of perpetual mistuning.

VOLTS FRO MTHE BLUE. Four nations are to-day battling to bo first in the field with the perfection of tho latest wonder of science—the transmission of power by wireless. They are Britain, the United States. Italy, and Germany. Professor A. M. Low, who has been investigating this possibility for several years, revealed to a London reporter the stage to which experiments had already been carried. “Every time you use your wireless set power is broadcast,” he explained. “The great difficulty to be overcome is the volume of power which can be transmitted.

“Not long ago Marconi told me he ' elieved that radio power transmission was a. distinct possibility. “Recent tests made by Tosia, the Italian Inventor, have brought a great leap forward. “Eventually the ‘projection’ of power by radio will be accomplished through a network of transmission staffers dotted over the country. “They will pick up power from one or more central stations of tremendous power. By increasing 'voltages and frequencies to an enormous extent it will be possible to overcome the problem of distance. | “Ships at sea would be propelled! along a radio ‘lane’ of power, aeroplanes would have their electric mot-j ors fed by wireless in a similar manner.

“Homes could be warmed, aud even clothes heated in Winter, by radio power on tap from a central station,”

NOVEL DUTCH PLANT. MASTS MOVED ON WHEELS. An engineering feat which sounds more like an extract from a. fantastic novel by H. G. Wells, than an actual accomplished fact, is now in operation in connection with radio station PCJ, at Hilversum, Holland. It consists of an aerial system which enables the station to switch its beam from one part of the world to another in a few moments, simply by revolving the complete two-masted aerial structure.

Up till now the method of directing die energy of a transmitter in one direction only —and that used by the BBC in covering the whole of the British Empire —has been to have a separate set of masts and aerials for every direction in which it is desired

to broadcast. Not only is this exceedingly costly, but \unlcss a. special set of masts is constructed for every part of the world, it is impossible to direct the beam sharply enough for many countries. But in Holland the engineers of transmitter PCJ. have built two aerial masts mounted on huge cars, which run on a circular track. The two cars

! are connected by a steel bridge, pivot- - ed in the centre and the entire struci titre may bo quickly rotated on this - pivot in such a way that the beam may ■ be sharply directed toward any country in the world. Previously, the idea of revolving aerial masts was rejected by American engineers on the ground that the scheme was impracticable. An interesting feature is that all around the circular track signs are to bo found, each bearing the name of a country, as "Australia,” “Brazil," “China,” etc. These signs mark the exact position for the masts in order to broadcast to the countries concerned. POWER. INCREASED. The new aerial system is not the only feature contributing to PCJ’s improved transmission. The station’s power lias recently been increased to 60 kilowatts in tho aerial, thus making it one of the most powerful shortwave stations in the world. It has been calculated that this transmission strength, combined with the new beam aerial, has tho same effect as the radiation of a dipole aerial operating with a power of 2000 kilowatts! The alterations affected by PCJ coincide with the station’s jubilee. Just, ten years ago PCJ carried out the first short-wave world relay, enabling listeners in the four corners of the earth to hear the chimes of Big Ben. A few weeks later another successful short-wave transmisison was carried out by PCJ —a broadcast. which made it possible for Royalty to address its subjects throughout the world. On this occasion the Queen of tho Netherlands spoke before the microphone of PCJ, and this broadcast was also received with great success. Although PCJ was closed down for a temporary period, having performed its task as a pioneer, even the new station, PHI, with its outstanding programme feature, cculd not eclipse the sentiment in favour of PCJ, which opened again in 1934. In spite of tlie fact that the number of shortwave transmitters now amounts to hundreds, PCJ and PHI are still counted favourites among many thousands of shortwave listeners.

Tho popularity of PCJ and PHI is understood when it is realised that their shortwave programmes are coiiducted in seven languages. Mr. Edward Startz, chief announcer, can speak seven fluently. His versatility and cheery personality have made him a popular favourite in many lands. PCJ, the pioneer shortwave station of the air, and a firm favourite with Continental listeners using its revolutionary aerial on wheels, transmits a special direct beam programme to Australia and New Zealand every Tuesday night. DOUBLE OPERA CAST. in England an interesting innovation in televised opera was made in the production of act 2of “Tristan and Isolde” with two casts —one to mime tho action before the camera and the other to sing the words. Dallas Bower, the producer, believes that the Wagnerian ideal of perfect sympathy between action and sound can be. more easily achieved by television than in tho theatre, where the demands of the music are so great that it is rarely possible Io combine first-rate singing with :i. standard of acting worthy of it. With, television, however, it is possible for the “visual” actors to give their full attention, to tho stage “picture," while the singers are free to concentrate on a perfect rendering of the music.

Tho experiment also made possible some significant innovations in the treatment, of operatic scenery. Instead of the action being confined to tho front of a castle, as in stage versions of the opera, hunting scenes, televised against a background of trees in Alexandra Park, were interpolated in the transmission. Consequently the visual actors were given considerable freedom of movement, while their parts were being sung off-stage. MYSTERY “STATIC.” About foui’ years ago it was found that a form of “static” was heard on a wave length of about 11.6 metres, t'ho disturbance apparently coming from a part of interstellar space. It was thought that there was some absorbing and radiating “black body” somewhere in the stellar system, but the results of investigations carried on since the first discovery and made available recently show this theory is untenable. An explanation of the origin of the mystery signals is still being sought.