RAIDO AND ITS RECEIVERS.

Sun (Auckland), Volume I, Issue 143, 7 September 1927, Page 12

RAI DO AND ITS RECEIVERS.

Conducted for THE SUN by

C. M. Taylor, B.Sc., A.M.I.R.E.

RADIO IN THE COUNTRY The writer has had the opportunity of a radio trip round the North Island, and at the time of writing is as far as Wanganui. It seems a remarkable fact that, as one gets out into the country, the number of aerials immediately diminishes very rapidly, and no matter how* small the country town is in its immediate vicinity, one sees aerial outfits, large and small, o»nate and simple. The question immediately crops up: Whom does radio benefit most? Surely the answer is: The farmer? He gets entertainment, news:, commercial market reports, delivered daily into his own home, no matte:* how remote he may be—in fact, he is brought very much closer into touch with things, almost as close as his fellow'-citizen in the town. In America the number of farmer listeners compares very favourably with the number in the towns. What is the reason? Is the Yankee farmer more prosperous, or more alive to his opportunities? Does the fault lie with the enterprise of our radio dealers? That is hardly likely. Is the service at fault? Of a number of farmers who have installed radio sets, one and all were pleased and satisfied with the service of the Broadcasting Company and with the service rendered them by their dealers. RADIO IN TARANAKI The writer had the pleasure of meeting several members of the executive of the New Plymouth Listeners’ League, namely, the Mayor, who is president, Messrs. Quickfall, Payne, and Lynch. This association holds monthly meetings, and caters for the social side of radio rather more than is usual with such organisations. The listeners in New Plymouth were informed that 2YA was the station calculated by the Broadcasting Company serv e their needs, but unfortunately 2YA with its greater power is very much inferior to IYA, and in consequence there is a great deal of dissatisfaction with 2 YA. The writer personally tried out the two stations in both daylight and evening transmissions. IYA on a polar twin two-valve set simply romps home at good loudspeaker strength in the afternoon, but 2YA is not even, good phone strength. At night the same applies, the volumes being increased, of course, but 2YA is not nearly as good as 2FC on the same two-valve set. This, in the writer’s opinion, is a matter of locality. The football broadcasts were listened to last Saturday on the same set at both Stratford and Tilth am, and in these two places 2YA showed its real strength. There is no doubt that the public in the country towns is beginning to look to these sporting transmissions as one of the main features of the “Saturday afternoon in the village.’ Crowds collected round the various demonstrating machines, and many kind remarks were made about radio. 2YA showed a bad tendency to blast almost all the time. Whether the announcer was carried away by the excitement of the match, and shouted into the microphone., or whether he was placed 100 close, one does not know, but his descriptions were not as clear as the voices of others in the vicinity. MR. HARRIS IN NEW PLYMOUTH Mr. A. R. Harris was to arrive in New Plymouth on Saturday night to meet the local listeners, an ev:nt I which shows that the company is at last going to meet its clients. The I local executive has asked for a relay i station at New Plymouth, but with ! only about 250 licences in the neigh- j bourhood the precedent it would ! create among other districts makes the writer doubt the reasonableness of |

such a. request. If the local league could put some sort of a proposal to the Broadcasting Company, such as a guarantee that it would undertake the operation of such a station as the old IYA, pick up programmes from IYA, 2YA, etc., and re-broadcast them, and in addition guarantee that the increase in the number of listeners would justify such an expenditure, then the Broadcasting Company would surely give such a proposal due consideration. With the cost of two operators, high studio rental, programme organiser, and expenses, the cost of operation of the old IYA was about £3O a week. This could probably be reduced to about £ SQO per annum, and if the New Plymouth league could collect 500 new listeners, then they would surely have an excellent case to put for a relay station.

It is remarkable how business men have taken up radio as a side line. One expects it from the electrical dealers, but why will they call themselves radio engineers? Also, motor dealers might be expected to dabble in this new province, but one gets a surprise at finding radio goods alongside confectionery, drugs, and —most strange of all—in a tailor’s shop. A HIGH STANDARD All dealers between Wanganui and Auckland were unanimous in the statement that the listening public must have good sets. This is an excellent feature, as nothing will keep listeners away from radio as poor reproduction, and cheap electrical goods never give service or satisfaction. The outcome is that the writer has not seen a “junk” set offered for sale in any dealer’s shop—an excellent state of affairs. MEW SCALE OF FEES Most of the hotels have radio installed, and most of those without it appear to be contemplating installation, but the new fee of £5 for such an installation is not going to encourage this type of listener. It seems a great lack of foresight, as it is surely a better thing for radio to have many sets in country hotels, giving entertainment, and introducing a large number of people to radio, tl an to have an occasional one. The larger number at the lower fee would be a better proportion from the “boom radio” idea as well as from the financial viewpoint, which includes > he licence fee, the new' - dealers which will spring up and pay their fees, the extra Customs revenue, etc. RADIO IN THE SCHOOLS New Zealand will watch the new experiment proposed by the Education Department to use radio as a means of instruction. There are many possibilities in this direction, but the field is at present rather limited in its application to such subjects os literature and music. Interesting travel talks of various parts of the world would make wonderful history and geography lessons, but they must be given by the right type of person, preferably a teacher of experience, wlio has actually seen the places. A NEW RADIO BOOK A new book, “The Elements of Radio Communication,” by O. F. Brown, M.A., B.Sc., reached. THE SUN last week, and should appeal to the student of radio. The whole subject is treated in a scientific manner, and —what will appeal to many—mathematics are used only where absolutely necessary. As Admiral Sir Henry Jackson says in his preface to the book: “As one who has no mathematical abilities, but has been closely connected with practical radio work since its original inception, I can confidently recommend this book to those who

wish to get a clear understanding of this useful and fascinating art.” GRID LEAKS The grid leak is one of the most unobtrusive components in a wireless receiver, and perhaps for this reason it is often bought and fitted without much regard to its construction. Frequently considerable trouble will I e taken to choose a good transformer or variable condenser, yet anything consisting of a tube with contacts at each end will be accepted as a grid leak. Unfortunately, it is not possible to determine w hether a grid leak is good or bad by inspection only, though some idea can be got by careful examination of its construction. The repute of the maker is perhaps the best guide of all.

The function of the grid leak, as its name implies, is to afford a leakage path for electrons which reach the grid of the detector valve, and wotild otherwise have to remain there owing to the imposition of the grid condenser, which blocks their path of escape. One would be inclined to think th*t anything in the nature of a leak vould serve, but this is not so. For good results the resistance of die leak must remain constant under working conditions, otherwise the component will be irregular in action, which will have a bad effect on the rectifying properties of the valves. Obviously, this constancy of resistance will not be secured by a component made of incorrect material, or badly designed. Originally leaks of fixed resistance only were made, but since the development of new circuits, in which the value of the grid leak is fairly critical. the demand for a variable grid leak has occurred. For ordinary “straight” circuits there is ittle ; eed for a variable leak, since modern valves are not at all critical with regard to the value of the grid leak. Summing up, fixed grid leaks should be— Reasonably accurate, say within 3 0 or 20 per cent. Absolutely constant in resistance under working conditions. Preferably mounted in a sealed or exhausted tube. Designed with an efficient contact between resistance element and end caps. WIRELESS INNOVATION The development of resistance-capa-city coupled amplifiers having anode, circuit resistances of some megohms in value, has led to the design of valves specially suited to these new conditions. The Mullard P.M.IA, P.M.3A and P.M.58 have amplification factors of nearly 40 and, in consequence, if the anode circuit resistance be, say two or three megohms, the amplification per stage is equal to that obtained from a transformer coupled amplifier. These valves take 0.1 amp. maximum filament current and are designed to work from 2, 4 and 6 volt L.T. supplies (for P.M.IA, P.M.3A and P.M.58 respectively). For reception of the local station, two P.M.IA or two P.M.3A valves may be used followed by a P.M.2 with two volt accumulator or P.M.4 with 4 volt accumulator. For stronger signals, the Super Power Valve P.M.254 should be used in the last stage when using a 4 volt accumulator. With two P.M.58 valves the amplification obtainable gives very considerable signal strength from the local station and in most cases it is desirable to employ P.M.2 56 in the “power amplifier” stage, although P.M.P can be used. Grid leaks should be fairly high and sufficient negative grid bias should be used on the power amplifier to ensure that distortion is not introduced in the last stage of the receiver. The characteristics of these valves are as follow: P.M.IA P.M.3A P.M.58 Max. Filament Voltage 2.0 4.0 6.0 Filament Current (amps) 0.1 0.1 0.1 Max. Anode Voltage 125 150 100 ■"Anode Impedance (ohms) 72,000 63,000 <4,000 ■"Amplification Factor 36 35 37 ■"Mutual Conductance (m/a volts) . . . - 0.5 0.55 0.5 •At Anode Volts, 100; Grid Volts, zero.