RADIO

Southland Times, Issue 21089, 22 May 1930, Page 14

RADIO

MAKING RADIO HISTORY. ■ TELEPHONE TALK TO LONDON. MACDONALD AND SCULLIN. EXTRAORDINARY SUCCESS. Sydney, April 30. Wireless telephony between England and Australia became an established fact on Wednesday, April 23, and astounded, by its extraordinary success, hundreds of thousands of listeners-in all over Australia, says the correspondent of the. Auckland Star. Mr Scullin, Australian Prime Minister, spoke to Mr Ramsay MacDonald British Prime Minister—a conversation described in parts as a model of early Victorian politeness. Mr Win. Hughes spoke to Mr Lloyd George—a conversation described as a crackle of Welsh with a modicum of studied English. Australian editors spoke to London representatives; and, most significant of all,.one Sydney' newspaper was able to beat all its rivals with scores of Australia’s first cricket mafch in England. Alan Kippax, one of the Australian Eleven, spoke from the ground at Worcester to the editor of the Daily Guardian, and gave the score then as Worcester all out 131, and Australia none for 30. At that dime the cables had the scores Worcester six for 111.

What this means in the swift receipt of i big news items from abroad may be conI jectured. Its effect on the costly cable I network is another aspect of the develop- : meat that suggests a possible loss in one I direction, with an incalculable gain in anI other. The First to Speak. I The first conversation commenced at 5.20 p.m. (Sydney time). After the British Post Office had announced the introduction of Mr Ramsay MacDonald to Mr Scullin, the following conversation ensued: — Mr MacDonald: Hello! Is that you Mr Scullin ? •Mr Scullin: Yes. Is that you, Mr MacDonald ? Mr MacDonald: Yes. How are you? Mr Scullin: I am well How are you? Mr MacDonald: Very well, indeed. Mr Scullin: That's fine. Mr MacDonald: It is such a great pleasure to establish personal contact with you again, and with all our friends in Australia. It is a long time since we met, and a great many changes have taken place since then, and it is also a tremendously great privilege, Mr Scullin, to be the first to speak at the inauguration of the telephone service across the thousands of miles that separate us. “I am sure also, Mr Scullin, that this achievement will be the means of knitting our two countries closer and closer together,” proceeded Mr MacDonald. “We

are now adding the hard spoken word to our Commonwealth bond, and, you know, there is nothing more attractive titan the spoken word. These are days of annihilation of both time and space, and I am now looking forward to the hour, and I hope it is not far distant, when we shall halve the physical distance between us by the establishment of the through-service by air for passengers and mails which has already been talked -of. We also hope that before the end of the year this telephone service will be further extended so as to give communication, via London, between Australia on the one hand, and the greater part, of Europe and the whole of the Central American continent on the other. When this has been accomplished the telephone subscriber in Australia will have access to over 90 per cent, of the telephones in the world. What an age, my dear Mr Scullin, we are living in. What would our grandfathers have thought of it! The Cricket “Ashes.” “By the by, Mr Scullin, this 'ashes* business! We are delighted to have your cricket team, and we are giving them a great welcome, hoping that hospitality given in the most lavish way may have some influence on cricket scores. You understand what I mean. “I would also like you to know how very sympathetic we are on this side of the world. We have ben watching the difficulties of your present economic situation in Australia. We appreciate to the full that your actions taken to deal with that situation have been dictated solely with the view to righting your present position and we'earnestly hope that your difficulties may soon be surmounted. • “Now we have not got long to speak, but I promised to say a few words on this occasion on the recent work of disarmament.” Mr MacDonald said that war had been called murder. “It is not,” he declared. “It is suicide. The- greatest menace to a nation is its own notion of security. B. CLASS STATIONS. POSITION IN AUSTRALIA. ' .Much interest attaches to the Commonwealth Government’s policy concerning the future of the B class stations, which are now 'providing excellent free entertainment over the air. The Postmaster-General (Mr Lyons) has before him a number of applications for licenses in all the States. Melbourne Trades Hall Council is anxious to conduct a B class station, and there have been enquiries by groups of church organizations, music houses, and trading firms. Melbourne Trades Hall, it is stated, will secure a license, and thus be on the same footing as union headquarters in Sydney. The problem of the B station is one which the Government is having some difficulty in solving. It desires to give a fair deal to existing licenseholders, organizations which desire to get on t ho. air, and the public.

Listeners who heard the splendid programme given recently by the Orphans’ Club Orchestra, will be pleased that the orchestra will reappear at IYA in June.

A.C. SCREEN-GRID. INCREASED SENSITIVITY. CONTROL OF VOLUME. The new A.C. screen-grid tube is not capable of producing better results when used by itself, says the Dunedin Star, but when intelligently used provides a new and efficient help to allow of noticeable improvements to be incorporated in a receiver designed to take advantage of the particular operating characteristics of this tube. When the A.C. screen-grid tubes were first made available, the most that was expected in operating improvements was increased sensitivity with the use of fewer radio frequency amplifying stages and the omission of the neutralizing or balancing means which are required for the ordinarydesigns of tubes to prevent feed-back through the internal elements of the valve. It developed, however, that other noteworthy improvements were possible, such as improved selectivity, along with the increased sensitivity, and the providing of the necessary high radio frequency gain to operate a power detector efficiently and to provide linear action in the detector for improved reproduction from the new highly modulated transmitters. Also the higher amplification has made commercially practicable the latest refinements of radio; automatic volume control and visual tuning.

It must not be overlooked that, while the screen-grid has overcome the feed back difficulties encountered within the valve proper, all other feed-back paths encountered in previous designs of tuned radio-fre-quency receivers remain, and unless these are “blocked” in the several parts of the individual radio stages by highly- developed shielding and by careful by-passing and filter systems, it is not possible to use' the higher gain provided by these new tubes. This means that the receiver must be a complete new design from the bottom up and any attempts to use screen-grids without the above mentioned precautions will fail to provide any material advantages over those of a receiver designed for the standard three-element valves. With the increase in sensitivity, possible in the screen-grid receiver come greater difficulties in obtaining complete and continuous control of volume from- that of a local station to that of the weakest signal of a distant station. Care must be taken to avoid audio distortion as well as broadening of tuning in the attempt to cut down volume to a whisper when tuning in on a local. Some of the higher-priced receivers use a system which can be likened to the j four-wheel brakes of a modern motor car, | the actuation being through the movement of one control with two separate and distinct restraining means in the circuit. This double-acting volume control leaves nothing to the judgment of the user.

Another manual volume control scheme is the use of an aerial switch to reduce the

sensitivity of the receiver in one big step and then through a single volume control knob to obtain continuous, although limited control of the volume in each. step. Unfortunately this type •of control requires judgment on the part of the user in order to avoid audio distortions, and in going from Weak to powerful stations, and vice versa, the aerial switch must be operated in addition to the regular volume control knob.

As stated, the increased sensitivity provided by the use of A.C. screen-grids allows for efficient application of “automatic volume control.” This type of volume control usually depnds on the strength of the broadcast station carrier for its operation, and can be made to maintain a predetermined loud speaker volume for big variations in signal strength. This -avoids the accidental crashes of volume when tuning from distant to local stations, as well as the maintaining of a definite volume level for distant stations, regardless of ordinary fading.

In this particular design of screen-grid ■ radio received the automatic volume control ■ is applied to the radio frequency stages and , the constants of the circuits are so selected as to protect the detector valve from overloading. The volume setting for the loud speaker is adjusted manually by a control that acts in the audio system, and when once set for the desired volume of reproduction, need not be changed for regular operation of the receiver. A CONTROVERSY. QUESTION OF GRAMMAR. A correspondent —and not the first—has written taking The Post to task for using the word “broadcasted” instead of "broadcast.’’ The contention in favour of the latter form is that the past tense of “cast” is “cast” and not “casted,” and that the compound verb should follow the same form. It is a question that has been much debated and does not offer itself easily to a final decision. One difficulty is that the-,word, as a conjugated verb, in common use, is so new as to have none of that grammatical history upon which such points are decided by’ grammarians. To sow seed broadcast is a very ancient activity, but there the word is an adverb; and though the farmer readily says “broadcast the seed,” he is much more likely to say “I sowed it broadcast”.than “I broadcast (ed) it.” A similar dispute has long been in progress over the word forecast, which is much older in popular use. In I that case, some grammarians gracefully concede the claim of “forecast” for the past I tense, on the ground that the verb came j into literary use before the noun, so that I the habits of the verb “cast” predominate: | had the noun been the older they would , defend the final “ed.” The shorter form is also preferred on the ground of euphony. .These claims cannot both be advanced for ’“broadcast,” but many people think it more euphonious than . “broadcasted,” though this is, of course, purely a matter of taste.

And in matters of taste a certain amount of obstinancy is apt to enter. In speech, of course, one can switch about'according to the tastes of the listener and the dictates of tact, if any; but in print it is another matter, and printers have, a god called consistency in whose worship they backslide as rarely as possible.. The shorjer form will probably win in the long run.

PROBLEMS OF FADING. ELIMINATION OF TROUBLE. USE OF SEVERAL AERIALS. Fading Is, of course, often in evidence on the normal wave-lengths at present used for broadcasting, particularly in connection with the more distant stations; but on short-wave working it becomes a real bogey writes Mr J. C. Jevons in Modern Wireless. Curiously enough it grows less noticeable as the working wave-length is increased, and practically disappears altogether from transmission on 2000 metres and over. It has been definitely ascertained that one cause of the trouble is clue to interference between the “earth bound” energy and the “space wave” component reflected back from the Heaviside Layer. Since the “space-waves” reach the point of reception by a longer path than the “earth-bound” waves, there is usually some phase difference between the two. Sometimes both waves arrive “in phase” and one gets very loud signals, and sometimes they arrive “out of phase” and signals disappear entirely. Then for periods the signal strength varies between these two limits, and so there' is a constant and irritating fluctuation'in the volume received. Another cause of alteration in signal strength arises from changes which occur in the polarization of the carrier-wave as it is reflected from the Heaviside Layer. This, again, causes the effective strength of the received wave to vary from a maximum or “in phase” to a minimum or “out of phase’’ condition. One remedy that has recently been successfully employed to counteract- fading effects, particularly in short-wave systems such as the beam, is to use a number of different receiving aerials separated by a short distance but connected together to a common receiver. Three aerials are each separated from the others, but all feeding a common series of valve amplifiers. In these circumstances at least one of the three aerials is bound to be receiving “in phase” signals, even if one or even both of the other aerials are for the moment only picking up,partly or wholly “out of phase” energy. Accordingly, there will always be some signal components being fed to the common receiver.

To emphasize the effect of the received signals a local oscillator is-inserted in parallel with all three of the valves. The particular aerial that is most effective at any moment reduces the resistance of one of the rectifiers and so diminishes the negative grid bias applied to the corresponding amplifier valve. This in turn allows more current to pass through that valve from the local oscillator and so increases the potential drop across an impedance which actuates the recording instrument or telephone.

Another remedy that has been found useful in diminishing the effects of fading is to impart a slight “wobble” or frequency variation to the carrier-wave. This tends to “average out” the effect of phase variations •at the receiving end and to maintain a more I constant level of signal strength. Similarly I a directional “wobble” may be used in or- J der to neutralize “reflection” effects at the j Heaviside Layer. In other words, instead ’ I of a beam of waves being transmitted in a : steady direction, the inclination of the beam is constantly varied slightly, upwards and downward-, over a narrow angle. Finally, the effect of using two different kinds of aerials simultaneously has also proved beneficial. HIGH TENSION BATTERIES. ALL-ELECTRIC RECEIVER. The all-electric receiver is gradually displacing the battery set, but at present there are still quite a number of the latter in use. The general use of p6wer valves has very considerably increased the load placed upon H.T. dry batteries, and the ordinary small-sized H.T. battery that could be relief upon in the earlier days to give six months’ service with, say, a three-valve set using ordinary valves, might only last four months .when a power valve is used for the last stage in the same three-valve set. Consequently the best manufacturers of H.T. dry batteries have introduced various sizes of battery—e.g,, small, medium, and large—while some even produce a larger size still, called the super. For ideal reception the high-tension voltage should be at a steady value, but unfortunately when dry batteries are used and much current is taken from them, as in the case of power valves, the i voltage slowly decreases and eventually the internal resistance of each cell becomes so high that it is incapable of main- i taining anything like a steady voltage, and the internal resistance of the cells may : have the effect of coupling two low-fre- | quency stages together and so setting up a - howl in the set.

High-tension batteries are often the cause of . mysterious faults which arise in sets, such as a low whistle,’ a marked tendency for the set to oscillate, buzzing noise, cracking sounds, etc, all of which are attributable to a worn-out H.T. battery. These are the reasons that have led to the production by manufacturers of varying sizes of H. T. battery, and while the larger ones naturally occupy more space and cost more money, they arc, in the long run, the most economical to buy. A battery twice the size will give more than twice the useful life under ordinary circumstances. The time the battery lasts naturally varies with the number of hours the set is used each week, and the length of life that individual users obtain from their batteries naturally varies considerably. It pays to buy good Ik T. batteries made by a firm of repute. A good battery involves the use of plenty of chemicals of .service quality to overcome the effects of polarization, and requires careful construction to guard against intercell leakage and short. The actual size of the whole battery is unfortunately • not always a safe guide to its “effective size..’’ and it is all too easy a matter, to mount a number of very small cells in a comparatively large container, fill up with black wax compound, and create the impression that it is a full-size battery. Actually it is the size of (he individual cells that count, and not the size of the container, and many of the so considered “cheap” H.T. batteries on the market are far from cheap in the long run. Small cells, poor insulation and bad construction soon lead to the battery being run down, and probably two good batteries will i last longer than, three cheap ones. |

Investment of the extra outlay involved in purchasing a battery of repute and of a size suitable to the type and namiber of valves used is a sound policy, and one that leads to economy in the end. In comparison with H.T. accumulators, H.T. dry batteries save a lot of bother in connection with charging and topping up the cells with acid. In the hands of the expert or enthusiast H.T. accumulators are quite good, but they are likely to prove expensive and inconvenient to the non-tech; nicaT minded listener, and, of course, on account of amount of space required cannot be used , in portable sets. Th“e other alternative, mains units, are quite good where electricity supply is avail- I able, but' unfortunately tonal quality is sometimes liable to suffer due to the presence of a slight hum. To sum up, buy a H.T. battery of a size suitable to the set. and buy one bearing the name of a maker of repute. SHIP TO SHORE/ FURTHER DEVELOPMENT. INSTALLATION ON MAJESTIC. A further great step in the development I of electrical communication Is now a com- ' mercial possibility, following the complete I success of an experimental public service [radio telephony inaugurated bv the White Star liner Majestic on her last outward and homeward voyages. The wave length used depends on the distance to" be covered and the hour, shorter waves being used for the longer distances and during daylight. The. wave lengths actuallv employed on the Majestic installation are 33, 26, and 17 metres, the latter being found most satisfactory for daylight working over long distances. In the Majestic’s transmitter the highfrequency carrier wave is’generated by a crystal controlled master oscillator operated on a quarter, of the radiated frequency in I order that a comparatively thich crystal I may be used. The output from this master j

oscillator is passed through a balanced amplifying stage, which entirely prevents

the frequency irom being affected by subsequent operations in the transmitter. The frequency is then quadrupled by two harmonic generators connected in its final power by two stages of h.f. amplification, each comprising two thermionic valves connected in push-pull. Modulation is effected on the first of these amplifiers, a modification of the Heising or choke control method being adopted, which enables the carrier to be completely modulated. The final power amplifier valves are of the water-cooled type and have an output of 2kw each. Together with their associ- ! ated tuning circuits and the rubber hose coils used to lead the cooling water to and I from their anodes they are contained in I a separate unit approximately 4ft square I by 7it high. ■ The remainder of the apparatus mentionled above, together with the modulating ' equipment, is all contained in another unit of the same size. The energy required to work the transmitter is obtained from motor generator sets run from the ship’s mains. | An interesting feature is the special spring lloor which has been provided to isolate the delicate apparatus contained in the transmitter from the vibration-of the ship. The jeceiver - works on the super-hetero-dyne principle. It comprises two stages of high frequency amplification, employing screened grid valves, followed by a first detector, beating oscillator, live stages of intermediate frequency amplification, sound detector and one stage of audio-frequency amplification. The intermediate frequency amplifier is made with the high degree of selectivity required for successful duplex working. In order to overcome fading—that is, periodic variation of the strength of the received signal—an automatic volume control is used. This consists of a special detector valve connected in parallel with thesecond detector, and so arranged that the strength of the received signals varies the grid bias on the first detector. A strong signal increases the bias on the first detector and so reduces the amplification of the receiver. This is accomplished by using a separate high tension battery for this valve and connecting a resistance between this battery and earth. The potential across this resistance is applied to the first detector.

The receiver is arranged in the form o a number of units assembled on Durahimi. trays, with-front panels carrying the meter and controls. The whole is assembled in teak cabinet approximately 3ft long, 2f high, and lOin. deep. As a protectio: against vibration rubber cushions are pro vided on the base, together with shock ab sorbing springs for wall mounting. The transmitter is located in a positioi beside the after funnel,- the aerials usei for transmission being rigged between th funnel and the mainmast. The horizonta half-wave type of aerial is employed, con sisting of a horizontal wire slightly less that half the wave-length long, broken in- th middle by a tuning coil across which is con nected the high frequency transmission lin< used to excite it. This consists of a pai of wires, spaced about Gin apart, leadini down to the transmitter. Separate aerial are used for each transmission wave-length The receiver Is located just above’ tin bridge, and the receiving aerials are rigget between No. 1 funnel and the foremast The operator in the receiving room has t variable amplifier and a visual volumi indicator which enables him to adjust thi level of the speech and send it over thi line to the transmitter. He can also ad just the volume of the received speech. The ' arrangement at the shore end of the circuit are similar to those employed on the short wave transatlantic circuit between this country and New- York. . The ransmitter employed at Millmortor (Rugby) is a “Standard” Type 111 equip ment, differing only from that used on the Majestic in that a further stage of h.f power amplification is added, using two 15 kw water-cooled valves in “push-pull” operating with an anode potential of 10,000 V obtained from a rectifier system. This is mounted in a separate unit similar to that housing the final stage of the ship ' set. The receiver at Baldock is \ large equipment designed primarily for use on shore at the receiving station of a longdistance radio link. Like the ship receiver, it'is of the superheterodyne type, but it is not portable. ! REGIONAL BROADCASTING. SYSTEM IN SWITZERLAND. Switzerland is to have a “regional” broadcasting system, somewhat .similar to that which is being instituted by the British Broadcasting Corporation, with three highpower stations—in the German, French, and Italian-speaking sections of the country respectively—and smaller delay stations where required in the principal towns. The most powerful of the new.stations, a Marconi type “P. 8. 60-KW. broadcasting transmitter, has already been ordered from Marconi’s Wireless Telegraph Company, Ltd. and is to be erected at Munster, about twelve miles to the north-west of Lucerne. This station will constitute the main “regional” station for German-speaking Switzerland, which is the largest of the three lingual sections ’of the country. While it is similar in design to the transmitters at the London “regional” broadcasting Station at Brookman’s Park, the Munster station will employ greater power, with 60-KW. in the aerial, compared with London's 30-50-KW. It will thus be one of the most powerful stations in Europe, a condition rendered necessary, in spite of the comparatively limited area served, by the fact that Switzerland, with its valleys, high mountains, and curious screen effects, is one of the most difficult countries in the world for broadcasting. Studios in Berne, Zurich, and Basle will provide the programme for the Munster station, which will be allotted the wave length of 459 metres. To provide for “crystal listeners” in the . towns, Marconi broadcasting stations of j-KW aerial power are to be erected at Berne and Basle. These stations are of special design, with crystal-controlled drive to ensure constancy sf frequency. The new station at Berne will replace the present Marconi 1-KW. “Q” aroadcasting station which was^erected in 1925, and which will later be modernized

and re-erected elsewhere to play a part in the “regional” . plan. At Basle ( the new station will be the frontier town's first fulltime broadcasting station, the broadcasting service having previously been carriea out by the Marconi transmitter at the Basle aerodrome, which is primarily employed for wireless telephony with aircraft. The re-organization of the Swiss broadcasting service on the “regional” basis is expected to be completed in 1931. This Is the second recent Continental broadcasting reorganization in which assistance has been sought from the experience of the British Marconi Company in September last year the company having received an order from Poland for high-power and relay stations designed to give crystal reception throughout the industrial and thicklypopulated district of that country.

NO EARTH. WILL HARM ACCRUE. i “My wireless set will give better results without an earth. Australian stations coming in very well. Will any harm accrue through using it this way?” writes “hootbailer”.in the N.Z. Herald. No harm can follow if no earth Is used, and many sets work quite well without one. It will almost always be found, however, that this is due to some error in the design of the aerial tuning circuit, and that if this is corrected the reception is much improved by using the normal earth connection. But if reception is satisfactory without it there is, of course, no necessity to make any change.