RADIO NOTES

Dominion, Volume 25, Issue 169, 13 April 1932, Page 14

RADIO NOTES

By

“ETHER"

CURRENT TOPICS (By Ether.) An enthusiastic low brow writes to say that he hopes as a result of the questionnaire we shall have less Bach and more bite. Wife: I got something good on your radio set at last, Bill. Bill: What was that? Wife: Thirty bob at the pawnbroker’s. • » * It is freely stated that the broadcasting authorities are very glum at having to find a total sum of £59,000 for the gear handed over to them by the original company. The board would not have so much to worry about if it was not necessary to pay out further large sums in order to bring its equipment up to the demands of to-day. Not even the most optimistic radio engineer could claim that the present plant at the various transmitting stations is the last word in modern design. Since our stations were installed, transmitting stations have improved enormously, especially in the frequency spectrum that they can cover. Every self-respecting modern transmitter thinks nothing of giving an even response curve from 50 cycles per second to 6000 or even more. Some do even better than that. After paying £59,000 for their stations, the Broadcasting Board will have to find somewhere in the vicinity of £20,000 or more if they are to give New Zealand new transmitters capable of putting over the high-class services enjoyed in other countries. On an income of, roughly, £BO,OOO a year, it is obvious that for some years the Radio Broadcasting Board will have to be extremely careful financially. Instead of being able to make wholesale improvements, as the public expects them to do, it is not unlikely that only small alterations will be possible.

The other theory has been exploded, and to quote Einstein, “Radios .etheral medium is fiction, a makeshift fabricated to explain something for which scientists have not had the correct explanation,” writes F. J. Martin. Steinmetz said, “Light and radio waves are merely properties of an electro-magnetic field of force which extends through space.” We kpow that light and radio waves will penetrate a vacuum, and this disproves the ether theory. If light and radio depended upon the ether for the propagation of their waves, how could they penetrate a vacuum? If science agreed that the theory of relativity is correct, the ether theory must be abandoned.

Aside from the numerous fine elements used in the construction of a radio valve, which could be termed analogous to minute girders, braces, cross-members, etc., there are 186 vari-ous-spot welds in the final assembly of the elements. This is equivalent to the number of welds required in laying a three-quarter mile pipe line, with each section of pipe 20 feet long. This would be sulficient to weld all steam and water pipe connections in the average home; or, in the marine field, to weld a mammoth anchor chain 93 feet long for one of the big ocean liners. In aviation, a complete ’plane, including the frame and fuselage, could be securely welded with this large number of operations.

The broadcasting of the Sydney Harbour Bridge opening ceremony was notable for the fact that one microphone was sufficient for all the broadcasting stations in Australia as well as a battery of public address loudspeakers, talkie films, ami gramophone records; The Bridge Celebrations Committee arranged that in the hands of Amalgamated Wireless should be left the control of the broadcast with the particular intention of avoiding the multiplicity of microphones, which is usually a feature of a gathering of such importance. It was the task of the engineers of A.W.A. to devise "means to ensure a circuit from which all the broadcasting stations interested could take a “split” without reacting upon each other.

The United States is, of course, the greatest radio country in the world from the point of view of numbers, and it is interesting to note the results of a radio census which was completed a little while back by the order of the last Congress. This showed that over 12,000,000 radio sets were in use in the 30,000,000 homes in the United States; that is roughly about 40 per cent. Since the count was made, however, it is estimated that another 4,000,000 radio sets have been sold, which brings tiie total to over 16,000,000. This means that evety other home in the United States now possesses a radio set. Taking the known average of 4.1 persons to the American family gives a total radio audience of over 60,000,000 people. The report in its final form shows that New York, Pennsylvania and Illinois each has more than 1,000,000 homes with radio sets, the total for New York being close upon 2,000,000. California ranks fourth, Ohio fifth, Michigan sixth, then come Massachusetts, Wisconsin, Missouri, lowa, and Minnesota.

DISTORTION TESTS Investigation by Anode Current Investigation of distortion by anode current is a subject in itself. It. is erroneous to suppose that fluctuation of anode current necessarily indicates distortion. A moving-iron or thermal indicator would show a fluctuation of anode current even under theoretically perfect operating conditions, and with valves as we have them a certain amount of pointer kick, even of a mov-ing-coil meter, is inevitable if appreciable output is to lie obtained, but excessive needle-swinging may be taken to mean gross over-loading (if tiie sound from tiie loudspeaker warrants that conclusion) or faulty operating conditions—battery voltages—or loss of valve emission. The amount of pointer kick manifested by a meter varies enormously for a given amount of distortion, according to tiie construction of the instrument. Some swing about quite violently when tiie actual distortion is tolerable, while others sluggishly refuse to recognise anything that is not already painfully obvious to the ear. One can judge to some extent from appearance which is likely to be tiie case; a light jioiiiter with a small coil is more likely to kick than one of large inertia. Also it. should hardly be necessary to point out that the same instrument will display more animation when run near fullscale than when the reading is low. WOODS’ GREAT PEPPERMINT CURE —For Inlhienz.:i, Colds.—Advt.

AIR NEWS SESSION Possible Improvements PRESENTATION AN ART Any newspaper sub-editor who insists upon filling his important pages with long summaries of shipping reports, weather statistics, and barometrical and other readings over practically the whole of one hemisphere, would be considered to have a poor sense of news value. Nevertheless, the radio authorities jog happily along as if the lay-out of the news they set before their people was not worthy of special thought. The usual lay-out of the news summary is to give the movements of every ship, vessel, and scow that is sailing from one New Zealand harbour and another. Indeed, this service has now been perfected and enlarged to give the names of everything afloat that by the chances may pay our Dominion a visit in the near future. Nobody will deny that this shipping report, ironically called a summary, is not of interest, but it is not of vital interest. Only a small percentage of the 70,000 listeners can be eagerly awaiting this report every evening, and the Radio Broadcasting authorities might well relegate the shipping summaries to a later period in the session. The same change might be made in the distressingly boring details concerning weather statistics from some twenty or thirty stations that feature so prominently in the 2YA news session at present. Probably the only piece of news unanimously wanted by every listener is the weather report itself. This weather report might well open the news session. The next thing to present is the burning news of the moment. For example, when Phar Lap elected to die in time for the first news session, why not tell listeners this piece of red-hot news at once? Actually what happened, so far as 2YA was concerned, was that we had to patiently wait while the announcer ploughed his way through the usual stereotyped weather statistics and shipping summaries. Indeed we had to contain ourselves while we were told that the Rangatira; which was tied up at its wharf at Wellington, was within wireless range of Wellington.

There can be little doubt that considerable improvements could be made in the presentation of the evening news reports. Sometimes one wonders if the announcer is doing little else but fill in time. For example, a gramophone item is vastly more entertaining than a long, quickly read extract from, say, the Simon report; that actually took 35 minutes to complete. Chunks of solid news like that require careful reading and re-reading. Shot through the loudspeaker they do not even go in at one ear and out of the other. Cannot the Radio Broadcasting Board be persuaded to believe that there really is an art in the correct presentation of a news session.

RECORDS FOR PICK-UPS Hints on Their Choice The choice of records for use, with a gramophone pick-up is not a difficult matter, unless the pick-up to be used with them is of poor design, states G.W. in “Popular Wireless.” A good pick-up, employed witli a good amplifier, can tackle any modern record and make of it a programme far and away more lifelike than can the acoustic gramophone. But if the pick-up, amplifier, or speaker of a radio gramophone outfit is off-colour, then tiie result is likely to be far inferior to the efforts of the acoustic machine. Electrical reproduction can aspire to far greater heights of “perfection” than the mechanical model, but it can also sink to even greater depths of distortion and music mangling. There are two reasons why the owner of a radio-gramophone may want any particular record. (1) Because he likes the item and wants to hear it well reproduced; (2) because he wants to use it as a test record to see if his outfit is doing its job properly. In tiie first case care must be taken that records having passages on them that are likely to show up badly, due perhaps to peaks in the pick-up reproduction, are turned down; if possible, other renderings of the same number being chosen. Such a course is difficult and somewhat unsatisfactory, but unless the pick-up and its associated apparatus are beyond reproach a certain amount of disappointment in the reproduction will be inevitable. Obviously, a brass baud record with plenty of high trumpet passages will sound horrible on a high-peaky pick-up. The second case, concerning the man who wants a record for test purposes, is very different. Here he will go out to find records having particularly I difficult or “peaky” passages in order

to help him to find, and subsequently to remedy, faults in his outfit. Organ records, beloved of salesmen or other demonstrators, do not as a rule assist in such fault-finding. On Mie contrary, they are what I call “foolproof” records. They have little top stuff and few really difficult deep notes (especially the cinema organ recordings) and so they are easy “to play” and are not likely to show up any weak features in the pick-up arrangement. For weak spots try tenor and soprano solos, heavy orchestral items, clarinet solos, brass bands, “brassy” dance orchestras, and piano recordings. Get a selection of these and you will soon find out. where your reproduction is at fault—and you are sure to get. some surprises. Incidentally, certain passages will make a good gauge of the improvement or otherwise, made by any schemes that you may try to better reproduction.

THE IDEAL SET Sacrificing Efficiency The engineer who was responsible for Britain's regional scheme, Captain I>. P. Eckersley, makes the following trenchant remarks on radio sets in “Popular Wireless” :— We seem to think that because a high-frequency valve has a theoretical magnification of 200 we ought to try and realise this value in practice. If we only thought to get (say) a mag. of 4 per valve and used three valves we should get (about) the theoretical mag. of one super-efficient valve. And if we used tuned circuits in each of these stages the mis-matching of the ganged condensers won’t greatly matter, and the shape of the response curve will approximate more nearly to an ideal than any we have to-day. Then, again, some dear theorist realises that two circuits reactively coupled produce a double-humped resonance curve. So we cry “band-pass.” Calculation shows that it is practically impossible to get selectivity for modern needs using just two circuits reactively coupled. Practice shows that the slightest mis-matching of condensers throws all theory to the winds; practice shows that there is nearly always some asymmetry in the response curves and that one may easily doublehump the modulation up to 100 per cent, or more. It is so typically short-sighted to try out these “pin-balanced-on-their-end” ideas and not get down to the robust common sense of the game. But, and it is a very big but, how can the sensible designer do what he wants to when the price of performance of valves is what it is? I do not think anyone will dispute the fact that the really multi-ganged valve-coupled tuned circuits give a robust solution to the problem. The sort of solution which says “hang efficiency! I want stability and common sense and ease of handling.”

MODERN LOUD-SPEAKERS Problems With Cone-types The transformation of energy from alternating current in the power valve to sound waves in the air is performed with great inefficiency by the loudspeakers commonly in use to-day. A review of the many experiments which have been performed to ascertain the ratio of acoustic output to electrical input leads to the conclusion that an average value for this ratio, which is a measure of the efficiency of transformation, is round about 1 per cent. The remaining 99 per cent, of the power is used up in resistance losses in the coils and in frictional losses in the moving parts. In fact, while it is easy to set the cone or diaphragm into motion, it is difficult to impart this motion to the air a little distance away. The speaker may be compared to a closed oscillatory circuit, which radiates but little of the power which it consumes until an aerial is attached. So far, with the exception of the exponential horn, which will be presently mentioned, no effective acoustic aerial has been devised for the loudspeaker. One cause of inefficiency is lack of rigidity of the cone. The light material, which must necessarily be used in order to obtain sufficient amplitude of swing, breaks up into vibrating segments at all but the lowest frequencies. Consequently, much power is dissipated in local circulation of air and less is available for radiation to a distance. If the cone is made smaller it becomes more rigid, and the local circulation diminishes in importance. But, unfortunately, as another cause of inefficiency sets in even with a perfectly rigid piston when its diameter becomes small compared with the wavelength of the musical note which is emitted. As the piston moves to the right the adjoining air is compressed in front and rarefied behind, and local circulation takes place round the edge in order to even up the pressure. The piston is not effectively loaded by the air.

DISTANCE LISTENING Securing Best Results When you are out for long-distance reception and selectivity—the two frequently go hand-in-hand —you want to take the greatest possible care of all the adjustments of the circuit. If you are using a screened-grid stage of high-frequency amplification, for instance, the anode circuit may be brought to the point of oscillation and the aerial circuit to the same state. In order to get these two critical adjustments, the voltages applied to the anode and the screening-grid of the valve must be adjusted with great care so that the greatest possible amplification can be obtained. The shielding in the set and also the provision of proper bypass arrangements become particularly important, and by careful attention to these it is much simpler to attain the critical adjustments mentioned above without running into oscillation. As regards the grid bias to be applied, it is important not to overdo this, but the exact grid bias voltage will depend upon circumstances. POWER VALVE VALUES We speak very vaguely about a “small” power valve, a “medium” power valve and a “super” power valve, but these terms have never been really defined and therefore different people interpret them according to different standards. The actual power which a valve will deliver to the loudspeaker is a quantity which it would be very useful for us to know. We often hear of a valve power of, say, 10 watts, but this does not mean that the valve will deliver 10 watts of useful power to the loudspeaker. On the contrary, the useful wattage for our purpose may be (and usually is) quite a small fraction of the actual power rating of the valve. A 10-watt valve, for example, may well give only 2 watts of power which we can make use of. The wattage of the valve refers to the power (generally in- the form of heat) dissipated at the anode when the valve is in operation. By the time you get the loudspeaker of the proper impedance in relation to the valve and you reckon the undistorted power output which you can obtain from the valve, this will probably turn out to be no more than one-fifth of the rated power of the valve.