RADIO RECORD

Greymouth Evening Star, 29 October 1931, Page 8

RADIO RECORD

NOTES FOR LISTENERS-IN

(By

“Reception”)

WIRELESS MARVELS. , VALVE CONTROL Hugh S. Pocock, editor of “The Wireless World, - ’ writing on September 4. in the “London Daily Telegraph.” stated: — ... The annual Radio Exhibition, which opens on Friday at Olympia, will be the ninth of'its kind since broadcasting began in this country, and will again be all-British in chaiaetei. When it is said that the exhibition is the ninth of its kind, it is not intended to convey that all the preceding exhibitions have been of equal importance. The wireless industry, it must be remembered, has grown from very small beginnings, and the first exhmition. held in September of 1922. was a very unpretentious affair by comparison with what the public will see

this year. The Olympia Show of 1031 will, by all appearances, create new rccoido for the wireless industry in every di rection. Business has grown meadilv from year to year, until to-day it can be said that there is no more progressive industry in this country than that which has been built up as the result of broadcasting. The exhibition will be open daily from 11 a.m. to 10 p.m., and closes on Saturday. September 20.

RADICAL CHANGES Although it has naturally, not been possible to inspect more than a very limited proportion of the new products of the manufacturers in advance of the show, yet enough has been seen to enable a general impression to be obtained as to the tiend of progress and to pick out what aie likely to prove to be the types of exhibits of outstanding interest. First of all, perhaps, should be mentioned the fact that in almost every class of receiver and all grades of accessories prices have been substantially reduced. and even in those cases 'where at first sight it may appear that a set this year is being sold at much about the same price as its

equivalent of last year, on closer inspection it will be found that this year’s set is much better value for money than its predecessor of a year ago. Externally a few sets may seem to be rather like the earlier types, but internally radical changes have taken place in meeting the need for greater selectivity. The increase in the number of stations in Europe and the higher power which is being used have brought about conditions of reception in this country where it is essential that receivers should be tar more selective than in the past, and to obtain this selectivity additional circuits, and in some cases additional valves, have been introduced into modern receivers. Just as in the past it has been customary always to speak of receivers in terms of the number of valves, now the practice is growing of indicating to the layman the degree of selectivity which may be expected from a receiver by revealing the number of tuned circuits employed. Sets employing special circuits and known as super-heterodyne receivers, ilthough by no means new in principle, hftve come into favour again in this country recently because of the extreme degree of selectivity which i can be obtain efl with them. A number c 1 ’ interesting examples of Ibis re|ce:ver will bo. seen at Olympia. The valve always plays an important part in tiie design of receivers, and amongst new valves there will be shown a type of special inteicst known as the “Variable-mu” valve, which ha" the interesting and valuable properly of increasing amplification with a weak station and reducing amplili-

cation automatically when an undesirably loud signal is tuned in. It is, in fact, an automatic volume control, and at least one of the new receivers this year will incorporate this valve. Much attention has been paid recently in the design of receivers to simplifying tuning and to making it easier for the layman to receive the foreign stations which interest him. and a number of new sets have- a tuning dial with the names of stations at the points round the dial at which these stations come in. Many receivers, although employing a number of tuned circuits, are yet controlled entirely from one tuning knob, the different circuits being precisely ganged together for this purpose.

NEATER RECEIVERS Neat appearance of receivers is an outstanding feature Ibis year. Much of the early unpopularity of wireless sets was due to the untidy appearance of the apparatus in the home: there were too many separate parts of a wireless set which had to be connected together with lengths of wire. All that kind of thing has been done away with to-day. and the most popular sets seem to be those of quite modest, dimensions which are entirely self-con-tained, even to housing the loud speaker, and. in many cases, being independent of an aerial for all general reception purposes. Manufacturers seem to have paid a

very great deal of attention to the design of receivers operating from electric light supply, and they have produced remarkably line results, but it is rather disappointing to find that so little attention has been paid to the requirements of that very large section of the communitj' which is still dependent upon batteries as a source of energy for the receiver. A great market undoubtedly exists for battery-operated sets designed to be efficient with economy in battery consumption.

Perhaps in the past it has been difficult to obtain, with these restrictions, the standard of quality in re- | production which the manufacturer has tried to maintain, but a new valve, one of the season’s latest products, is likely to have a pronounced influence on the design of battery sets of the future. This is a pentode type of output valve, working from a twovalve battery, .and, although capable of giving a very substantial input to the loud speaker, it is extremely economical in the consumption of current from the lI.T. battery. ENORMOUS VARIETY It is impossible here to attempt to go into detail regarding the enormous variety of sets and accessories which Olympia will disclose, but the advance information obtained, although incom-

plete, is sufficient to make it possible to draw a comparison between this year's show and its predecessors. Last year it may be said that for the first time manufacturers began to standardise and to look to the production of wireless receivers in quantity, designing the apparatus on proper engineering lines rather than assembling receivers in a box from a collection of component parts. The manufacturers have gained confidence. from past experience, and the sets this season will not be in the nature of “experimental models” exhibited to see if they catch the public fancy before the manufacturers risk making them in quantity. This year's sets will have been most thoroughly tried-out before the show, and by the time the public sees them they will practically all be in full production at, the factories, so that the exhibitor will be able to meet the public demand at once instead of having to wail whilst the sets are being produced.

SINGLE SIDE-BAND TRANSMISSION An important advance in the perfection of shout-wave single side-band radio-telephony was demonstrated successfullv last week at the radio station of' Le Material Telephonique at Trapes, near Paris, by the company’s engineers in co-operation with the research engineers of the International Telephone and Telegraph Laboratories of Hendon. England, at the station of the National Telephone Company in Madrid. A distinctive feature of the installation is a pilot, wave, which is transmitted solely for the purpose of keeping the distant receiver in tune with the transmitting station. Single side-band radio-telephony takes advantage of the fact that only pari of the ordinary wave is really essential for perfect reception, provided that the receiver is kept effectively tuned wiih the transmitting station. Inasmuch as frequencies of the order of LS.ouo.OOO cycles a second are involved. tuning presents a difficult problem, but it has been solved by use of the pilot wave. While short-wave single side-band systems in general are not new. the pilot wave system greatly improves the quality of transmission, reduces interruption, due to fading and atmospherics or interference from other stations. Nearly twice as many radio stations can be operated by the single side-band method than is at present possible without interference between them.

Radio engineers during a number of years have sought for practical means of applying the single side band method to short-wave radio, for its advantages have been proved in longwave radio as well as in wire communication. In fact, telephone administrations from the first have planned their short-wave radio stations so that this method could be applied whenever it became possible to <lo so. The technical difficulties, however, proved formidable, and the means previously used iu applying this method were not adequate for commercial application.

Experiments have shown that the single side-band system is practicable commercially, and it is expected that it will be put into operation on many of the important international radio telephone circuits. SHORT-WAVE NEWS The first attempt hi Portugal to provide a regular broadcasting service is now being made by Abilio Nunes dos Santos, Lisbon. The station, which is private, with the call sign CTIAA, is operating on 291 metres and 42.9 metres. Programmes on the longwave are broadcast at present, on Tuesday, Thursday, and Sunday from 9.20 a.m.. to 11.20 a.m. Now Zealand summer time, while the shortwave transmitter is on the air the same hours on Friday,. Announcements are made in Portuguese, French. English, German, and Italian.

The French colonial station at Pontoise is already “hard up.” M. Julien Maigret, director of the station, reports that colonial listeners are rather exacting. Their requirements are: Less music, absolutely no gramophone records, and more live news. Unlike the controllers of SSW, the director of this station must find his own programme material, and is under an obligation to provide eight hours’ original entertainment a day with a 'monthly expenditure of £l6O. Several listeners have reported a station heai'd at a. late hour at good volume, but from which no call sign has been given. The foilowing announcement was heard and reported by an Australian: “The station is for expcrimVnlal broadcasting on shortwaves. and is situated in the East indies. The power in the antenna is 1 kilowatt, and the wavelengths used are :Mondays, 49.30 metres; Tuesdays. 31.3 metres; Thursdays, 19.55 metres. The present schedule is from 10 to 11 p.nv., and from 11.30 p.m. to 12.30 a.m. on all wavelengths (New Zealand summer time, two hours later). Transmissions on the lower wavelength are only just audible in

Melbourne but on the higher waves reception is excellent.