THE WIRELESS WORLD

Otago Daily Times, Issue 22053, 8 September 1933, Page 3

THE WIRELESS WORLD

NEWS AND NOTES By Magna Vox. Items of local interest are 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. 2BL, Sydney.—Bss K.C., 353 metres. 2FC, Sydney.—66s K.C., 422 metres. 3AR, Melbourne.—62o K.C., 492 metres. SLO. Melbourne.—B3o K.C., 371 metres. SCL. Adelaide.—73o K.C., 395 metres. 4QG, Brisbane.—76o K.C., 385 metres. IYA. Auckland.—B2o K.C.. 365.8 metres. 2YA. Wellington.—72o K.C., 420 metres. 3YA, Christchurch.—9Bo K.C.. 306 metres. 4YA. Dunedln.—6so K.C.. 463 metres. ANSWERS TO CORRESPONDENTS. "Battery," Kakanui.—Yes, small twovolt accumulators, such as are used for radio, can be charged from big ones used in cars. It is also possible to charge up a small wireless battery over-night, in an emergency, by joining it up to the car's battery. In series with the radio battery, connect a side-lamp bulb which takes about half an ampere, and then join up the accumulator to the plug points, which arc usually provided nowadays on the dashboard of a car. Be careful to connect positive to positive. B. N., Dunedin —Values of plate and cathode load should be equal if exact balance is required, but probably there will be other variations wider than this. Generally, the bigger the by-pass condenser the better. The detector bias must be altered, otherwise you will always get rectification, and hence distortion when used as an amplifier. In the case of the second value, half the voltage is dropped in the cathode circuit and half in the plate circuit. Cathode will thus be at a high voltage compared to heater. Can the valve stand this: "Selector." Cromwell.—(l) Try altering the disposition or length of the aerial. Alternatively, place a small fixed condenser of, say, iOOOI mfd. in series with the aerial. If trap circuits are used there must be one for each source of interference. I am assuming, of course, that the sot is, in itself, sufficiently selective. (2) Short-circuit the grid-le;.k. If it disappears, the output stage is blameless, and the search must be carried further back in the circuit. NEW 3YA STATION. Work is now well under way at Geddies Pass, the site of the new transmitter to serve Christchurch, and incidentally Wellington as well. The first of the buildings to house the transmitter has now been completed well on schedule. It is understood that some 30 men are working on the job. The foundations for the masts have been laid. One mast, in fact, is now 60ft up in the air. When completed both masts will be 300 ft high, but the constructional work will go quickly ahead provided weather conditions do not interfere. It is perhaps interesting to add that these masts, when completed, will each weigh 75 tons. They are designed to withstand winds many times stronger than have ever blown in New Zealand. It is no secret to reveal that the radio authorities confidently expect this station to be open before the end of the year. , MICA CONDENSERS. Small mica condensers which play an important part in the radio receiver are now so cheap that we are apt to overlook the amount of precise scientific work that goes into their construction. The days have long since passed when any old bits of tinfoil and mica sheet could be slung together and called a condenser. In these days the condenser is subject to the most exacting conditions in use, and accordingly it has to be subject to similar conditions, if not even more stringent ones, in process of manufacture. It is no exaggeration to say that a goodclass mica condenser is really a precision component, and it is remarkable, having regard to the price, to what a degree ot accuracy these condensers are turned out. The condenser, for one thing, must not vary in its capacity appreciably with the lapse of time, it must not vary with atmospheric conditions, it must be lowloss," and it must, as already mentioned, be reasonably accurate at the start, and remain so during its working life. SUPERSET POSSIBILITIES. Many new possibilities are opening out, and it seems probable that the superheterodyne of the future will be as great an advance upon present-day technique as modern seta are on those of a few years ago Developments which appear probable are the general inclusion of ultra-short wavebands in the tuning ran<*e, the use of quiet automatic volume control systems, the adoption of ironcored tuning coils, the employment of metal rectifiers instead of valve detectors, and the inclusion of controllable selectivity and quality; some of these developments will, of course, be applicable to any type of receiver, but others will be practically usable only with the superheterodyne. It should not be expected tfiat these tendencies in design will be soon found; there are many technical difficulties to be overcome before they are realisable in a satisfactory form. Within the next few years wc may hope fo see most of them.

BAN ON MUNICIPAL STATIONS. The House of Commons recently refused to allow local authorities to establish broadcasting relay stations, by means of which they could supply their electric light users with alternative programmes. The controversy arose out of the Middlesborough Corporation Bill, which, it passed in its original form, would have given that local authority power to set up a relay station and give its hsteneid a choice of live programmes. Sir Kingsley Wood, the Postmaster-General, pointed out that if the Bill were passed he would have been compelled to give similar powers to othei local authorities. I lie objection to the establishment of this new principle was led by Mr Montague Lyons, who said that it would create a new form of municipal trading and interfere unfairly with private enterprise. Referring to the financial effect of the Bill, he said that a director, staff, and broadcasting house would have to be maintained and subsidised by the ratepayers of Middlesborough. He maintained that by entering on this plan the Yorkshire town would be competing with its own ratepayers who supplied radio instruments and machinery. Mr Kingsley Griffith supported the proposal, saying that the people of Middlesborough had not objected to a system under which they would be able to plug into the electric light wires and receive selected and amplified programmes. Sir Kingsley Wood pointed out that the Middlesborough Corporation's main function, would be to provide amusement. Despite the fact that the supporters of this plan thought they had the Postmaster-General on their side, the proposal was defeated by 144 votes to 48, and the effect of the vote will be that the scheme will be expunged from the Bill. ADVANCE IN DESIGN. . I am often asked by one hesitating whether or not to buy a new radio set, "Are there likely to be any revolutionary changes in set design? Should I, therefore, hold off for a bit? " says an English writer. My answer is always, "No! there will not, in all probability, be any revolutionary changes, so buy now. Ot course, this statement requires qualification. If one had bought a set in 1922 and not bought another until 1033, it would seem as if there had been revolutionary changes. The 1943 set will be very different from and very much better than the set of 1933 price for price. It depends largely, too, what you want in a wireless set. It is therefore impossible to qualify my statement that it is unlikely that anything revolutionary is going to take place in a way to satisfy all types of listeners. Looking back over more than ten years of development, I shall say that the major change in receiving set technique involves the giving of much the same result for a far smaller sum of money. The set of to-day, for a civen result, costs about one-quarter the price of the sot of five years ago. 1 he continuation of such a process is conceivable, but naturally one cannot imagine that the price of a set in 50 years time will be zero. It has always seemed to me a pity that, in general, the tendency has been to reduce price for a given result rather than to improve the result for a given price. Naturally one wants everyone to be able to afford wireless, assuming they derive some pleasure from

listening; but it is a rather sad commentary on the part of radio that manufacturers do not find a wider market for a better result. Of course there are many factors which make chea-pness the criterion of comparison between different makes of sets. In the first place, transmission technique does not allow even the best of receiving sets to produce a pleasant sound except when the set is timed to the local station. In effect, then, the set of the future may give to-day's result for a little less money, may, indeed, achieve its compromise more confidently, but it will never succeed, in raising the entertainment value of wireless much above the present level. Evolution —not revolution may, however, reveal a gradual change in the whole technique of broadcasting. It seems to me fundamental that somehow and some day' we must achieve a means of diiitribution whereby the listener has a far greater real choice between different typed of entertainment than lie _ can — owing to technical limitations—enjoy today. I. do foresee a time, long distant, no doubt, when the listener may have his entertainment "laid on" just as his water, electric light, and telephone is laid or. to-day. His only visible equipment will be, say, 20 buttons and a loud--1 speaker. The quality of reproduction will be far better than any enjoyed toI day; the ease, convenience, and scope 'will greatly transcend anything we know. ! But if you are determined to buy a new set do not hold back because you think I that just round the corner there is going I to be a revolutionary development in the I design of receiving sets. Things will I happen, but they will happen ever so I slowly—much too slowly. But they will I happen.

THE SUPERSET AND SELECTIVITY. In a superheterodyne circuit, as is well ' known, the frequency or wavelength of the signal is changed, and for the purposes of explanation it will be assumed that a signal of 1000 kilocycles, that is, 300 metres, is being received, and that in the frequency changing part of the circuit this frequency is altered to one of lOOkc, that is, 3000 metres, after which it is amplified in that part of the circuit which is known as the intermediate frequency amplifier, and then rectified or detected and handed on m the usual way to the output stage from which it is transferred* to the _ loudspeaker. In superheterodyne circuits there is at least one tuned circuit preceding the first valve, which is tuned to the signal frequency, and this circuit, which is probably associated with the grid of the first valve, has a distinct preference for the wanted carrier. Thus in this circuit the wanted signal is stronger compared to the unwanted signal than it was in the preceding circuit, which, in all probability, is the aerial circuit. If there are other tuned circuits the discrimination is carried still further until the unwanted signal is apparently removed. If this unwanted signal is relatively weak compared to the wanted signal a few circuits tuned to the signal frequency will do all that is required, but if the unwanted signal is strong it is necessary to have a great many tuned circuits at signal frequency or else adopt some other method such as the superheter-odyne principle, where the changing of the frequency to a lower value immediately provides a great advantage. To take an example—suppose that there is an unwanted signal _ at lOlOkc, which is, of course, in the neighbouring channel to the wanted 300-metre signal. The change of frequency that is made in the circuit means that, in the case assumed, the wanted signal becomes lOOkc and the unwanted signal 90kc. The difference before and after the change is still lOkc, so that there does not seem to bo any appareut advantage in making the change. But the selectivity of any circuit, that is, its ability to deal successfully with a signal which is not of the frequency to which the circuit is tuned, increases as the resonant frequency is lowered. In other words, if there are a number of tuned circuits all of equal efficiency, they will reject to the same extent all signals which differ by the same percentage from the resonant frequency, no matter whether that resonant frequency be at 1000 m or 100 m. This, of course, puts a different aspect on the Question. In the cases considered, the signal frequencies differ by 1 per cent., but after these frequencies have been changed they differ by about 10 per cent. Therefore, if the intermediate frequency circuits are as efficient as the signal circuits their task is much easier. Taking the figures mentioned above, provided that the circuits are of equal efficiency, that tuned to lOOkc can reject a signal of HOkc as easily as a circuit tuned to IOOOkc can reject signals of llOOkc. There is, however, an important point which must not be overlooked, for, although tho spacing between stations is, so to speak, increased about 10 times, the spread of the side-bands is likewise increased, and, therefore, the speech and music frequencies, which are usually assumed to extend skc on either side of the carrier frequency, have to be considered as extending about 50kc on either side of intermediate frequency. Unless great care, is taken in the design of the intermediate frequency circuits, the inherent selectivity, which is so great a virtue of the superheterodyne, may bring about serious sideband cutting and a loss of the higher speech and music frequencies. A bass band type of circuit or some correcting type of circuit is, therefore, necessary if good quality is to be obtained. In the earlier types of superheterodyne, trouble arose from lack of attention in this respect, but in present-day receivers there is little to fear, as designers have long since recognised the necessity for maintaining the quality of the reproduction.

HERE AND THERE. The British Broadcasting Corporation's Empire News Bulletin was being regularly received and much appreciated by members of the Mount Everest expedition when they were on the mountain. This news from men at the " top of the world" concerning the ease with which they were able to keep in direct touch with home is a tribute to the far-reach-ing success of the 8.8. C. Empire broadcasts. For the purposes of its Empire broadcasts the 8.8. C. works in five zones, and it would be the Indian, Ceylon, Malaya, and Burma transmissions that was heard. Each zone has its own range of wavelengths, which are used directionally, the particular wavelength employed being dependent on the conditions at the moment.

Exactly 10,809,502 homes in the United States were equipped with wireless sets on January 1 last, according to a special trade survey, constituting 50.2 per cent, of the total number .in the country. There lias been an increase of 4,760,000 in three years. The district of Columbia claims the highest percentage of set owners with 88.7, while New Jersey and Rhode Island follow with 83.1 and 82.1 respectively. New York can claim 79.4 per cent, of its homes, as radio-equipped.

The number of wireless licenses issued in England during May was approximately 289.400. After allowing for those which expired, the total number in force at the end of the month was 5.570,500. an increase of 40.500. During May 240 .successful prosecutions were undertaken, and the fines amounted to £243.

New Zealand visitors to Honolulu find that our main Dominion station, 2YA, is heard fairly regularly there with good volume and clarity, and its types of programme meet with much favour by those who make a point of tuning in the far south. This outside tribute to the quality of New Zealand programmes will bo gratifying to those responsible for them, and an indication to the general listening public that our standard is not so low as some jaundiced critics would have us believe.

The disadvantage of having tuning dials listed with the calls of stations instead of in degrees or kilocycles is emphasised by the fact that: 27 out of 34 European countries have adopted the new wavelengths laid down in the Lucerne Conference plan. All the British stations will alter their waves, but in the great majority of cases the alterations will be slight. The result, it is hoped, will give a freedom from interference which has not been enjoyed recently in Europe.

The Australian Broadcasting Commission is following a wise plan in appointing an Australian as its representative in London. The principal work of this gentleman is the choosing of new music, plays, operas, etc. New Zealand may not yet be able to afford a special liaison officer for broadcasting, but it might ar-

range for co-operation with tlie sister Dominion to secure some advantage from the Australian official's position and experience.

Broadcasts designed "to bring the American public a more complete. understanding of international relations, and to provide Europe, South America, and Asia with reliable interpretations of American thought," are being arranged by a Public Affairs Institute with the co-operntion of the Columbia Broadcasting System. The plan, which is to exchange more programmes with foreign countries, has the support of such authorities as Dr Nicholas Murray Butler, President of Columbia University, and Mr Alan Welsh Dullies, who was advising the American delegates at the Loudon Economic Conference.