RADIO NOTES

Dominion, Volume 26, Issue 69, 14 December 1932, Page 5

RADIO NOTES

By

"ETHER"

CURRENT TOPICS The world’s champion radio family lives in New Zealand, according to the American Radio Relay League. Not only are three sisters of the family qualified and active amateur radio operators, but there is also a husband and a young brother active in the game. Kathleen and Naney Kirby maintain the home stations (ZL4DT and ZL4FN) at Douglas Street, Balelutha. Their sister, Mrs. Peggy Cameron, operates her station, ZL4CL, at 40 Cargill Street, Dunedin. Her husband, Ewen Cameron, ZL4BJ, is one of New Zealand’s bestknown amateurs. It is understood that the radio authorities have practically finalised arrangements for a special broadcast to this Dominion from the short-wave Empire station. The programme consists of a tour round the whole Empire. Ships at sea will be spoken to, and listeners will be able to listen in to two-way conversations between the radio authorities in the various countries and the officials of the British Broadcasting Corporation. The following towns in the various parts of the Empire will take part ,in the proceedings:—Edinburgh, Aberdeen, Dublin, Belfast, St. John’s, Quebec, Montreal, Niagara, Calgary, Vancouver,- Wellington,. Sydney, Cape Town, and Gibraltar. This programme is timed to. commence at 2 a.m., Boxing Day, New Zealand Summer Time. It will. last about an hour, concluding with a message to the Empire from his Majesty the King. ♦ . * No fewer than eighty . per cent.. of Europe’s amateur ’ transmitters can converse in English. This is the illuminating result of an inquiry made by that organisation of ultra-efficient “ham" operators—the Ragchewing Club, savs an English writer. German and French are the only other tongues that are anywhere in the funning, and the hundred or so amateurs from all European countries who replied to the R.C.C. questionnaire emphatically emphasise their-preference to English. A few of them, incidentally, can claim fluency in no fewer than seven languages, including ancient Latin and modern Greek! Spanish amateurs seem to be least conversant with English. Few of them, in fact, can even make themselves understood in French, and “.Spanish only” appears to be the watchword with many. The Dutch, on tlie other hand, show remarkable cosmopoHtanism.' white Britain, although indicating a “French and English only complex, yet possesses many multl-llni gual amateurs. 4 FAILING SIGNALS About Meter Tests CHECKING VALVES Of the various ailments that occasionally afflict a receiver possibly the most prevalent is a general decline in its performance. Foreign programmes cnee received with comparative ease may now require more careful tuningin, reaction has to be pressed to its limit, and, in addition, the quality of reproduction shows a marked deterioration, writes H. B. Dent In the V^ re T less World.” Replacing the batteries, if these provide the operating power, teads to a temporary improvement only, ‘and the listener finds himself at a loss to account for the unsatisfactory state of affairs. Finally, yielding to expert advice, a new set of valves is obtained, and once again the receiver recovers its earlier liveliness. It is well within the bounds of probability that one, or maybe two only, of the valves had deteriorated with use, and if a few simple measurements had been made occasionally and a record kept of the condition of each valve, replacements could have been made when necessary and many months of unsatisfactory reception .avoided. The essential information can be gleaned by the judicious use of an inexpensive . measuring instrument —one of the combined volt-milliammeters would prove the most serviceable in the case of battery-operated 1 sets.. For with this not only- can the anode currents taken by the valves be ascertained, but the voltage of the .lI.T, battery checked from time to time. The meter should have a resistance of not less than 200 ohms per volt, , while the current ranges, of which there should be two for preference, should give full scale deflections with between 5 and Io mA on one range and about 30 mA on the other. Voltage measurements of the H.T. battery, if this is of the smaller dry-cell type, should be made with the receiver switched off, for the meter will draw some 5 mA for a full-scale deflection. A high-grade instrument "having a resistance of 1000 ohms per volt would give a far truer indication of the state of the battery since voltage readings could then be taken with the set working and the battery under normal load.

MATCHING VALVES A Push-Pull Problem SEPARATE BIAS Valve manufacturers are usually willing. to supply pairs of valves specially matched for working together in push- i pull circuits, and so it might appear that there is little point in making provision for separate bias control of each output valve. But there is another aspect in the matter that may appeal to the enthusiast in pursuit of extreme efficiency; all valves inevitably deteriorate in Use. and it is a fact that they do not always deteriorate at the same rate. Consequently, a pair of valves that are perfectly matched when new' may have appreciably dissimilar characteristics after a period of use. We hare here a further argument, in favour of separate bias control, as tbe performance of the output stage may be kept, at maximum by making an occasional adjustment as it becomes necessary. FUSES

lii determining the sizes of various fuses required, whether for mains or battery-fed receivers, the current which the circuit? may safely carry without damage should be considered, and not the current which normally flows. It should also be remembered that the charging current of a reservoir condens er may easily blow a fuse unnecessarily, and for this reason it is desirable to tit as large a fuse as possible compatible with safety. The fuses available.for wireless use are quite inexpensive, a. holder and a dozen spares costing- less than the price •rf one general-purpose valve.

MICRO RAYS Commercial Developments HALF-INCH AERIALS A micro-ray equipment giving radio communication on the shortest wavelength employed at any radio station in the world has been ordered by the British Air Ministry for use in connection with cross-Channel flying services. This equipment will be manufactured by Standard Telephones and Cables Ltd. in their Hendon factory. Some 18 montlft ago the first demonstration of practical radio telephony on a wavelength below one metre was given between Dover and Calais on a wavelength of approximately 18 centimetres by the same firm. 'V The equipment now ordered by the British Air Ministry will operate on an even lower wavelength in the neighbourhood of 15 centimetres. For communication on this minute wavelength, transmitting and receiving aerials less than an inch long are used. Microrays oscillating tit a rate of about 2,000,000,000 times a second are generated in a special miero-radion tube. These oscillations are led through the tiny transmitting aerial and are then concentrated by a combination of mirrors into a fine pencil of rays, . which are thrown into space from a circular reflector, about ten feet in diameter. This reflector is focused on. to a similar reflector at the receiving station. The equipment ordered by the Air Ministry will be located at Lympne Airport, near Hythe, and will operate in conjunction with a similar equipment ordered by the French Air Ministry to be. situated at St.- Inglevert Aerodrome, nearly seven miles southwest of Calais. It will be used for announcing the arrival and departure of aeroplanes that are not fitted with radio and for routine service messages. An extremely interesting feature of this new service will be the use of .teleprinters, both for receiving and Wansmitting messages. In this way typewritten messages will actually be sent across the Channel by radio, thus providing a permanent record at each end. The use of teleprinters will also help ‘to overcome' the language difficulty, since it is easier to understand a written message in an unfamiliar

language than a spoken one. Moreover, messages can be received on a teleprinter during the temporary absence of the operator. A great advantage of the use of micro-rays is the fact that they are almost entirely unaffected by atmospheric conditions. Another advantage is that on this extremely low wave band there is practically no interference from congestion of the ether or

from nearby machinery. It is expected that the station will be in operation early next spring, and its use will relieve the volume of traffic handled at Croydon and Lympne. SHORT-WAVES

& Reaction Hints BETTER DECOUPLING lit view of the increased interest in short waves resulting from the opening of the Empire station in a few weeks, the following suggestions bow to improve reception are well worth studying. Writing in an English journal tin expert says:— There are still many short-wave receiving sets, particularly in the batteryoperated class, which rely to a considerable extent upon the aid given by reaction for their reception of the weaker and more distant stations. With a well-designed set expertly handled reaction can enable something like miracles to be performed—but it must be reactions of the smooth and gentle • type. Nothing is more exasperating or more difficult to handle when one is searching for foreign stations than the set whose reaction is fierce or floppy. When reactioitjijs fierce , there is first of all a bu’Jd-itp in signal strength as the knob is slowly moved clockwise; then, just as it seems that good volume is about to. be obtained, the .set bursts into violent oscillation. If floppiness ;oy overlap is present oscillation does Vot cease until the reaction knob is turned back a good deal past the point at which it began. It is well worth while to spend a little time when a new set, either purchased or home-made, is brought into use over the adjustment of the reaction control. Since valves, even those of the same make and type, are apt to differ not a little from one another in their characteristics, as many detectors as are available should be tried with a view to finding whether one of them gives smoother operation than the others. Adjustment of the hightension .voltage may help considerably. But the cause of unsatisfactory working of the reaction arrangements is very often that the decoupling arrangements are insufficient. Where there is a 2-microfarad decoupling condenser in the plate circuit of the detector the addition of a second of the same value connected in parallel with the first is often surprisingly effective.

GRID BIAS Apart front tbe choice of a suitable valve, the most important factor from the point of view of economy is again the grid bias. Neglect of this factor is probably responsible for more prematurely exhausted H.T. batteries than fc uy .other cause. The grid bias is the sluice gate which holds in check the reservoir of the H.T. battery, so that it is sound economy to buy a fresh bias battery with every new H.T. unit.. The higher the negative bias the less will be the drain on tbe battery. and the experiment should be tried of increasing the bias until it is obvious that the quality of reproduction is impaired. Many sets are worked with an unnecessarily high H.T. current through neglect of this simple precaution.