THE WIRELESS WORLD.

Otago Daily Times, Issue 20905, 20 December 1929, Page 5

THE WIRELESS WORLD.

NEWS AND NOTES

By Macxa Vox,

Items of local interest arc 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.

Metres, 7ZL, Hobart ~ 535 3AR, Melbourne 484 4YA. Dunedin 463 2FC. Sydney .. .. .. ~ 442 2YA, Wellington 420 4QG, Brisbane 385 3LO, Melbourne .. .. 371 2BL, Sydney 353 2AB, Sydney 316 2KY, Sydney 280 ITA. Auckland .. .. .. 333 SYA, Christchurch 30(1 SCL, Adelaide .. .. .. 395

ANSWERS TO CORRESPONDENTS. Amateur," Milton.—The fading you complain ot js probably due to your leadin touching the side of the house or the aerial swinging against a tree or some other object. Keep your aerial well free of nil earthed objects and (< clean your insulators periodically. N.,” Roslyn.—There would be three tuned stages and a regeneration control. It would be necessary to have at least two controls (apart from the regeneration control), and it would be a_ difficult matter to- balance np the circuits to the detector. Try using a double drum dial tuning the first R.F separately and gauging the second R.F. and detector. G. -F O’C., Dunedin.—(l) No, it is not the aluminium panel that is producing hand-capacity, This fault is generally due to, faulty wring or spacing the parts. An aluminium panel, with components insulated from it, but connected with the earth terminal, is a safeguard against hand-capacity. (2) The best method of eliminating hand-capacity is total shielding, earthed. A fixed condenser placed across the telephones often eliminates capacity due to headphone cords in a , short-wave receiver. Often handcapacity is due to reversed variable condenser connections. The remedy ■ here is obvious. Keep coils away from condensers and also from the panel. The reason why the coils should not be placed near the panel is not because' the panel produces hand-capa-city, but because the hand is very near the coil when tuning, unless the coil is moved farther away from the panel. The field; from the coil passes ' through the bakclite panel unless a shield is placed over the coil, when is minimised. Some types of short-wave receivers are very sensitive, and suffer badly from hand-capacity, which is difficult to eradicate.

TUNING GAUGED CONDENSERS. When a number of circuits are being simultaneously tuned; by’means of gauged condensers, a diffifficulty sometimes arises owing to the natural capacity in the aerial circuit due to the’ aerial and earth. In these circumstances the transformer in the radio frequency stages or the aerial timing coil is apt to become tuned to a lower frequency ■ than the other circuits, and it is necessary 'to find some method for overcoming this effect. There are various ways in r , which this can be achieved, and perhaps the simplest of all is to leave the aerial circuit untuned and to introduce instead a choke coil (or resistance), connecting this between the grid and filament of the first valve. The radio frequency inter-valve coils arc tuned by the condenser, and consequently it is a very much simpler matter to arrange the settings. This scheme will not be applicable in all cases, but in a largo number of cases it provides a very easy way out of the difficulty and gives perfectly good reception.

NEW SPANISH STATIONS. British material, design, and workmana played a conspicuous part in the ing of the important new group of wireless stations which were opened this week by the King of Spain at Aranjucz, near Madrid, in _ the presence of the Marchcsc Marconi, the Spanish Prime Minister, and Ambassadors- representing other countries. This group of wireless stations has been designed and built to extend the range of Spanish external communications having regard to Spain's importance in the commercial life of the world and particularly of South America. Madrid is now placed for the first time in direct wireless telegraph communication with both North and South America and, by means of the Marconi abort wave beam installation which is included in the equipment of the Aranjuez station, a regular commercial telephone service between Spain and the , Argentine Republic will be available in addition to high-speed beam telegraph services. For use in these circuits special receivers have been constructed by the Marconi engineers on behalf of the .Transradio T.’sptnola, the Spanish Company to which these stations belong and which carries out the wireless telegraph services between Spain and other countries. The supply of this apparatus to Transradio Espanola is the second big order for British wireless equipment recently -received from Spain, the Marconi Company have also supplied,' a short wave station to the Spanish Government to establish a direct wireless service between Madrid and the. Spanish colony tic Fcrando Po, in Equatorial Africa.

"B ” STATIONS IN AUSTKALIA.

There is a possibijity that the Australian Government will sanction the construction of additional “B” stations in Sydney and Melbourne. A special committee has been appointed by the Federal Government to consider the whole question of broadcasting in Australia. It is not expected that the report of that commit.ee will bo available before the Federal Parliament rises for the Christnits vacation., In the meantime the Post Office Department proposes to renew the licenses 'of "B ” stations expiring this month, or early in the New Year, for a period of one year, subject to certaiu restrictions. Commercial organisations and fiiu)s_ in Sydney and Melbourne are pressing tiie Government for an early decision on the question of additional “B ” stations. It is pointed out that if the Government grants the requests there will be from six to 10 additional ‘B ” stations in Sydney and Melbourne; that the construction of the plant and erection will give additional employment in Australia, and that the programme competition that will ensue will add considerably to the number of licensed listeners in New South Wales and Victoria. Those interested in the radio industry believe that in the erection of extra “B ” stations will be rcuud the solutru of the prop lent arising from'the big cancellation of licenses that has taken place in New South Waits, Victoria, and Queensland during the past two years. In that period there have been at least 10,000 caqcedatons lit New South Wau-s, The cancellations were more than counter-balanced by the new licenses taken out, but the fact remains that many of those who cancelled their, licenses have not renewed them and so have been lost to radio as supporters of broadcasting and purchasers of sets and parts. The Port Office Department, on the other hand, is championing .the erection of “C " stations to’bo under the control of the department, and to be leased for certain hours daily or weekly to different firms or organisations. These, and other matters, are being fully considered by the Federal Government Wireless Committee. It is understood that the Federal Labour Party, as a body, favours a complete reorganisation of the present system of broadcasting in Australia.

STATIONS’ RESrONSIBILITY. Feu- radio cntlin.siu.sts appear to realise the tremendous responsibility which rests on our broadcasting stations. These transmitters have the work of creating a carrier wave modulated by the frequencies generated by the desired sounds in the studio, and these modulation frequencies must he as nearly a faithful copy of those in the studio ns is possible. Once the signals leave the transmitter a host of factors upset them to soma degree, Lon.-eqnonUy the received a lid reproduced signals never can be better than the-trans-mitted ones.. The broadcast, stations, therefore, are primarily responsible for tbe limitations of our reception. Tills sounds a most obvious sort of statement, but it-is strange the number of listeners who would not appear to have any appreciation of fi'? t: i - ■ r. Nle-ni-i tln-ir ro-'.-n-

tion become distorted, or should it be accompanied by a low drone, a continuous whistle, or all manner of sizzling noises, they are quick to suspect their receiver. I hey will bo justified ijv doing so on some occasions, but they will bo olf the track on many others. The essential work of the broadcast station is to make a big stir in the ether. The bigger the stir the better will reception be over any but the shortest distances —other things being equal. The amplitude or strength of the earner wave, however, is not the thing which controls the amount of “stir.” Many of our broadcasting station are high-powered in the sense that they have a powerful carrier wave, but they are ineffective because the modulation introduced by the music is so slight. Should these stations reduce their carrier output by four times, and increase the percentage of modulation by four times, their effectiveness would remain the same. Alternatively, should they leave their carrier power as it is, and increase the percentage of modulation by four times, the same big improvement would be obtained as when the carrier power whs quadrupled, the percentage of modulation remaining the same. Modern broadcast practice is not only to use a high carrier power, but a high percentage of modulation. In other parts of the world, for instance, we find a host of stations with a carrier output of 50 kilowatts, which can be completely modulated by the mVisic from the studio. This represents a usenil output or “ stir ” probably a couple of hundred times greater than the average .New Zealand station, Obviously, modern stations of that type are much more effective fn forcing their music through atmospheric and power leak interference than those typified by the equipment at present manufacturing bur radio signals.