RADIO RECORD

Greymouth Evening Star, 15 November 1934, Page 4

RADIO RECORD

NOTES FOR USTENERS-IN

( By

“Reception")

LOSS OF QUALITY WHAT ABOUT OVERSEAS? A contributor” the “Wireless World,” who, after each Olympia radio show, commits himself to some outspoken ’comment on his impressions. put in a few words in Ins latest article for the “local station receivei. I think it is becoming evident that progress, not only in the public taste, but in the plans of the manufacturers, is being made, and that the time is not too far distant when broadcasting will come into its own (he writes). However much one may « contrary, it cannot be denied that the broadcasting art implies, first, the securing of artistic talent to perfoim certain evolutions within a specially prepared room; secondly, the translation of the sounds resulting therefrom into electrical impulses which arc propagated in all directions by means of a transmitting station over an area whose size is determined beforehand by the design of the station; and, thirdly, the reception of these impulses by a receiving set, and their final conversion into sounds in the listener s home. It must be obvious that any discrepancy between the original sounds and the reproduced sounds is interfering with the proper enjoyment of the original-broadcast programme. By an accident of Nature, known as the Heaviside layer, the signals from a station can be received at greater distances than the design of the station will normally permit, and this is where “the fun begins.” Although, probably, none of us has ever met a non-swimmer so eccentric or nervous as to wear a diving dress at all times in case he accidentally falls into or wishes to enter the water, yet there are millions of otherwise quite sensible people who purchase radio sets whose designs completely destroy any inherent ability the sets might possess to reproduce a local station well, because they, the public and the designer, think that they will avail themselves of the accident of Nature already mentioned. As is well known, the great majority of the public will buy a wireless set in much the same way as they would buy a cat or a parrot. One cat or parrot is enough for the average home, and, judging from the experiences of my friends as well as myself, one brace of regional stations is enough for the average home, too. I do not deny that foreign stations are received throughout the length and breadth of this country every night, but such procedure is limited. If, therefore, the ability to receive large numbers of foreign stations means a reduction in the quality with which a Ideal station’s programme can be reproduced, then the purchase of such a set by the average man is an act of folly; these acts of fplly are committed every day, to the gratification and' profit of the mass-production set makers.

SOUTH AFRICAN RADIO South'Africa is now in process of deciding whether or not it will go 8.8. C. Hitherto its broadcasting service has been privately provided, and apparently, notwithstanding good intentions, not very well provided. It is a vast country. At Cape Town there is a thoroughly modern station which throws most of its power overboard into the sea, and bumps a good deal of the rest up against mountains. A thousand miles away to the north is another station, with nothing between but a large scattered population that would like to hear good broadcasting but cannot. And this is a country which is one of the great “static” areas.

A very interesting move was made by the Cape Government in regard to a possible change of policy, for it invited not a mere engineer, however eminent, to come from London, but Sir John Reith himself, director-gen-eral of the 8.8. C. The last mail brought news of Sir John’s arrival at Cape Town, but he had only just landed and was cautious about saying anything, even as to whether the adoption of semi-State control would be wise. Sir John Reith has never set himself up as an authority on the technical aspects of broadcasting and is not likely to offe% South Africa a coverage plan, the drafting of which must be full of difficulties; but he will probably be able to give some sound advice on the general policy, and he will certainly have enjoyed his trip.

AMALGAMATED WIRELESS The twenty-sixth annual report of Amalgamated Wireless (Australasia), Ltd., states that: In the course of the year’s business, the company had distributed by way of wages and salaries among its Australian employees more than £300,000, and it had contributed to the revenue of various governments a total sum of £160,000. The company’s operations had also been of assistance by purchasing the goods and services of other Australian enterprises, in respect of which the company during the year under review paid to other companies and to Government departments a total sum of £225,000. These figures were quoted for no other purpose than to emphasise the fact that this undertaking might reasonably claim to have assisted in that very important economic function of keeping money in circulation within the community. Such' figures helped them all to understand how one successful undertaking benefited many other undertakings by purchasing their goods and services and by supplying purchasing power to all persons directly or indirectly . employed in connection with this undertaking.

WIDE-RANGE SYSTEM. A DIFFICULT PROBLEM Broadcasting authorities and receiver manufacturers are at present devoting some attention to the development of what is known as ‘ high fidelity” or “wide range” systems of transmission and reception. This development is in keeping with what has happened on the other side of the world, and, as the term would imply, it is concerned with the extension of the audio frequency range of the transmissions. The problem is a difficult

one, more particularly for receiver manufacturers. ( What the probable outcome will be it is not easy to forsee, but this desire to improve reproduction should be of material benefit to broadcasting in general. The danger is that “high fidelity” may become a more or less meaningless catchword, as other phrases have been in the past. From the point of view of the transmitter an expansion of the audio frequency band means that very careful attention is necessary in the design of studios, microphones, land lines, and the other equipment associated with the transmitting process, including methods of recording, the construction of records, and pick-ups. It is not an extremely difficult matter to design such systems successfully, but they are more expensive than those which are content with a narrower range of speech and musical frequencies. The receiver manufacturer has perhaps a more difficult problem than the transmitter, because selectivity and fidelity are inseparably associated. A receiver which is likely to be called upon to operate in any part of the continent and is expected to pick up without interference stations of various powers, which may be only a few miles away or as many hundreds of miles away, cannot hope to reproduce a wide band of speech frequencies. Each station is given a channel which is but 10,000 cycles wide —that is, 5000 cycles on each side of its assigned wavelength or frequency.' If it could transmit speech or musical frequencies higher than 5000 cycles it would intrude into adjacent channels. Likewise, the receiver which is designed to reproduce frequencies in excess of 5000 is likely to pick up some of the frequencies included in the transmissions of stations in adjacent channels. In other words, a receiver - designed to cover a musical range of 10,000 cycles must pick up more than one transmission if those transmissions are close together, and, at the receiving point, are of comparable power. There is also the question of interference, such as that from electrical machinery, and from natural causes, such as static. The situation considered is perhaps an extreme one, and the difficulties are not so great in a city such as Sydney, where the eight local stations are fairly well spread through the frequency band, and at present have no very close or powerful stations in adjacent channels, but if, for example, at night time signals from more distant stations are sufficiently strong there is the possibility of high-pitched heterodyne whistles due to interference between carrier waves of adjacent stations and a “twittering” kind of intermittent noise, variously known as side bandsplash or “monkey chatter,” caused by the side bands of one station interfering with the side bands or carrier waves of another. The chances of this kind of interference being present depend entirely on the relative strengths of the signals of the wanted and unwanted stations in the receiving locality, which means that it is not safe to guarantee that any particular station could be received properly everywhere, assuming that its transmission included the required wide range of frequencies. It appears to be virtually impossible for a receiver to be designed which can always provide “high fidelity” reception without interference. The only solution is the inclusion in the receiver of some means for varying the selectivity so that the best compromise between quality and freedom from interference can be obtained at will. • This would mean that when local stations were being received the response could be widened, and, provided that there was no interfering signal present in sufficient strength, the reproduction would be sufficiently good for most practical purposes. When long-distance reception has to be relied upon the selectivity would be increased and the quality impaired. Besides this necessity for varying selectivity, the receiver would also have to include means for handling the wide response properly, which, amongst other things, would mean a very carefully designed speakei - or a battery of speakers. In short, the instrument would not be cheap.

WAVE FORMS Although it is apparently a simple type of sound, a noise such as the report of a revolver is harder to deal with faithfully than many musical notes. The wave form of a sound such as this has a very steep front and a relatively flat top, so that, instead of the wave following a fairly smooth and periodic curve, it resembles more a series of rectangles or squares. Although they do not appear to have any particular curve associated with them' it can be shown mathematically that such a form can be analysed into a multitude of frequencies extending from zero to infinity. The component frequencies cover a wide band and include a greater number of individual frequencies than a more musical sound. For instance, a noise may include a fundamental of 50 cycles per second, plus all the odd harmonics; that is, vibrations, of 150, 250, 350 cycles, and so on up to frequencies in excess of 20,000. Such a sound, therefore, applied to a broadcasting system is a very severe test of the microphone, the rest of the transmitting equipment, the receiver, and the loudspeaker, not only for their ability to respond quickly to a sudden change of current, but also for their ability to deal with a wide range of frequencies, because unless the higher harmonics are present, the characteristic form and sound of the wave are lost. Unfortunately, no system can handle successfully every frequency from zero to infinity, nor even every frequency which is audible to the majority of people. Further, every electrical circuit has a property which is equivalent to inertia in mechanical devices. A mechanism such as a flywheel requires considerable effort to set it ini motion quickly, and likewise requires considerable effort to bring it to rest

quickly. This is because every mass desires, as far as possible, to remain in its original state, whether that state be one of rest or one of motion. In a similar manner any electrical circuit, and more particularly one in which coils and chokes are included, 1 does its best to keep constant the value lof the current flowing therein. It offers considerable opposition to a rapid increase and also to a rapid decrease. This property of circuits is known as inductance, and in some cases it is of great value. Most of the sounds that have to be handled by the broadcasting system are of a complex form. Their complication is largely due to the fact that, in addition to the fundamental frequency, there are always a certain number of overtones or harmonics which give the speech or music its distinctive quality and enable a listener to distinguish between the same note sung by a soprano or other singer or sounded by a flute, piano, violin, or other instruments. Thus, a note which has a frequency of 256 cycles per second may have associated with it in varying qualities harmonic frequencies of 512, 1024, 2048, 4096, 8192, or more cycles per second. The combination of frequencies such as these results in a wave from which, instead of being relatively smooth from crest to crest, has a number of intermediate peaks and troughs, as well as their dispositoin, being governed by the number and strength of the harmonics or overtones that are included with the fundamental note. Besides these variations in form, there I are always large changes in the aver- . age magnitude or volume of the transmission. No item, whether it be I speech, song, or a combination of instruments, maintains a constant volume for anything but a small fraction of a second. Abrupt changes are always present, and form an essential part of the reproduction. For example, in speech, words beginning with letters such as “p,” “t,” or “k” cause sudden changes in volume, while the report of a gun, the clapping of hands, and other noises produce similar results. These types of sound which rise abruptly to their maximum value and fall perhaps equally rapidly again are known technically as “transients.” As the name • implies, the sound or wave is something which is of fleeting nature without! any lasting or sustained characteristic.