THE WIRELESS WORLD. BROADCASTING FROM AEROPLANE.

Otago Daily Times, Issue 19903, 24 September 1926, Page 5

THE WIRELESS WORLD.

BROADCASTING FROM AEROPLANE.

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. LOCAL NOTES. A running commentary on the match Canterbury v. Hawke’s Bay, played at Christchurch last Saturday, -was broadcasted by 3YA, Christchurch, during the game. The transmission was received well here, and several good reports are to hand from local listeners-in. Mr H. C. Frame, of Kaikorai Valley, who operates a two-Valve Roberts set, tuned into the transmission, and reports that he heard the description clearly with the 'phones, although it was barely loud enough for the loud speaker. It may be noted that play in the Wellington-Canterbury match, at Christchurch to-morrow, will be broadcasted by 3YA. That fine station, 2FC, Sydney, will begin broadcasting on a 432 metres wave length shortly instead of on HOC metres, as previously. This news should be welcomed by many enthusiasts who were hitherto unable to listen-in to this station. 1 A GREAT SHOW.

The National Radio Exhibition, which is now open at Olympia, is claimed to be the greatest display of wireless instruments which has yet been seen. Two previous exhibitions which have been held were private, but this one is public, in response to great growth of popular interest. Receiving seta for the home undoubtedly oiler the greatest attraction to visitors, and these have become the subject of increasing ingenuity and development. The tendency is towards simplicity. In the design of loud speakers the hornless type or disc seems to be more popular. With a large vibrating surface giving a softer tone and more even distribution, it is preferred for the drawing room. Sets that are a mass of screws and wires have practically disappeared. Many self-contained seta are on view. Aerial and earths and all other paraphernalia are being eliminated. Portable instruments are more frequent. HINTS AND TIPS, A dial that wobbles as it rotates does not affect the working qualities of a radio receiver, but it certainly does spoil its appearance. When you buy dials have the dealer spin them on the shaft of a condenser, and make sure that they run true before you make your purchase. It is often possible to true-up a dial on a shaft by fitting a bit of paper or shim brass in the shaft hole or by polishing the shaft on one side or the other with emery paper. Never' .use water for washing the panel or any part of a radio receiver. If the panel gets dirty or greasy dampen a soft cloth in alcohol, and rub it lighty over the surface to bo cleaned. This will remove the dirt and grease, and upon drying it off with another clean cloth it will leave a beautiful smooth polish without in any way damaging the apparatus. The alcohol evaporates rapidly. If you have a loose connection in your set that makes a jarring or rattling sound in the headphones or loud speaker it would be well to lift up the lid and investigate each wire to find out which one may be loose. Use a small wooden rod for moving the wires while you have a station tuned in. By pushing the wires with a rod slowly back and forth you will hear a loud sound when you move the one that is loose. Then you can tighten it at the binding post, or solder it fast whore it is loose. Never use a metal screwdriver for this purpose, ns you may short-circuit the “A” and “B” battery connections and blow out all your tubes. Never fuss around the insides of any radio receiver with a screwdriver when the batteries are connected. One drop of acid from the battery will rum a ’phono or loud speaker_ cord. The acid eats its way into the fabric covering, and finally weakens the cord so that it breaks at that point. It would not bo so serious if it ruined the ’phone cord at once, for a new cord does not cost much. The trouble is that it usually causes sizzling and crackling noises and weak signals for weeks before the source of the poor recontion is discovered. , Wherever possible, the ground-lead should be kept as short as possible. Extended ground-leads not only broaden the tuning of a set, but they add resistance to the antennae circuit. The receiver should be located as near the ground connection as the arrangement of the furniture in a room permits. KEEP AWAY FROM POWER LINES. When you install your aerial wires bo careful that they do not run over or under any electric wires or cables that may bo in the vicinity. Do not place them near any such wires, because the wires themselves may carry high-voltage currents, and if they fell on your aerial they might conduct the high voltage currents down to your receiver while you were tuning in. This might subject you to a severe shock. Keep your antennae away from such lines and prevent accidents. THE WORK OF THE AMATEUR. The opening of the big station in Auck-; land recently suggests some thoughts oh the history of broadcasting in New Zealand. It is not a long history, but it is a verv interesting story. Prior to 1924, wireless—apart from naval and military wireless and the ship to shore commercial communication —was a very tame affair. Amateurs throughout the Dominion had been dabbling in it for years —even before the war. But it was not until about 1920 that any radio telephony work was done. Some of the more skilled amateurs were experimenting with it, and their efforts were not confined to the transmission of speech. Gramophone records were transmitted by wireless, from one amateur to another, interspersed with plentiful “hullos” and comments on the quality of the transmission, modulation, power used, etc. Some of those transmissions were truly frightful exhibitions, but the perfection we know nowadays was not known, and indifferent transmission was accepted and passed as successful amateur broadcasting. For some reason or another, it was always referred to as a “test” or “experiment”: “This is 3AB testing; the next record will be a Sonora record, ‘0 Sole Mio,’ by Oaruso.” Presumably the Postal Department only licensed the amateurs for experiments and would not countenance any transmission that was not a “test” or “experiment.” There were comparatively few listeners, as the habit had not been developed. and the cost of component parts was excessive. For instance, a valve which now costs about 15s, could not be bought under 4Cs, and they wore very scarce at that. The listeners also had to make their own sets; there were very few, if any, radio traders who sold complete sets ready for use. In 1921 and 1922 the “concerts" given by those amateurs grew in number and attractiveness. The possessor of a receiving set proudly invited his friends to his home to listen to the wireless concert, and was not at all perturbed bv any caustic comments on the quality of the music produced by the set. Too far credit cannot bo given, however, to the amateurs whose efforts were the beginning of broadcasting in New Zealand. None of them foresaw the immense strides that would be made in the next few years, and no one dreamt of a station so powerful and so efficient as IYA, Auckland. There were a few large companies engaged in wireless business, but they left it to the amateur to sow the seed that was to produce a very rich harvest for them, and incidentally to, inaugurate and foster a movement which_ is now a source of entertainment and delight to thousands of lisfeners-in in Australia and New Zealand.

WHAT TUNING IS.

Tuning anv radio pet is a matter, first, of adjusting the value of capacity and of the coil connected to the aerial and earth leads to make that circuit respond most readily to the wave length at which the station to be received is operating. This may sound complex at first, but in reality there is no difficulty for the listener, who does not have to worry over technicalities Ho need only know that an increase in either the condenser dial reading or in the number of turns in the coil, or both, will cause the circuit to respond to a higher wavelength. So if a station is heard loudest with the condenser at minimim i* is probable that a smaller coil will allow the station to be more compWdv tuned in with a lower dial rending, which is. of course, advisable. If, on the other hand, the condenser dial is at zero and still the music cannot ho tuned to a “peak.” the substitution o! a smaller ceil Ktm tl* use (tf more condenser will over-

come the difficulty. It is this balancing of the value of the coil and the condenser that forms the basis of the major tuning process in the radio set. Probably the receiver will have a secondary circuit, and the same proceeding will hold good in this case. Should the set be fitted with one or two stages of radio frequency amplification there will probably be a similar number of additional circuits which to be tuned in the same manner. Should the receiver be one of the latest pattern two or more of the condensers in these circuits will be mounted on the same shaft, and the complication of having to tune each separately is therefore overcome, -the fact that human beings have two hands only has contributed to this move to reduce the number of tuning controls, and a limit at two such controls is very desirable, in such a case the aerial condenser can be operated with the left hand, the second dial with the right hand, and the two moved in unison, keeping both circuits tuned to the same wave length as a •‘search” is made for the wanted station. In order that this “searching mav bo done effectively there are two other controls which must be first adjusted in an approximate fashion. The most important of these is the “reaction”—controlled by a dial or knob variously marked “stabiliser," “regeneration,” _ ‘ tickler, or “volume.” The exact functioning of tins control will vary in different receivers, but the effect will be essentially the same. Energy will be fed back from the output of the detector valve into the first section oi the receiver, so producing powerful ampli fication in addition to that provided m other ways. Py careful adjustment of this control the receiver is made extremely sensitive, and in a condition to reproduce a distant programme if the tuning dials are adjusted to the right wave-length. Over-adjustment, however, must be carefully avoided, since radiation can readily be produced and neighbours reception seriously interfere with. Such a condition is usually indicated by shrieks _in tne ’phones or speaker which vary in pitch as the tuning controls are varied.

THE NEUTRADYNE CIRCUIT. The neutrodyne circuit employs radio frequency amplification, and ideally each stage of radio frequency is a one-way relay which passes the incoming power only in the one desired direction. However, on account of the proximity of the plate and grid, and filament ot a vale to each other, there is always present a certain amount of coupling between the output and the input circuits of the amplifier. This coupling in effect causes a slight amount ol regeneration or feed back through the capacity between the valve elements, unless special devices are used to neutralise it. One way of neutralising or balancing the capacity coupling through a valve is that of tho neutrodyne. In almost all radio frequency amplifier circuits there is present some inherent regeneration, even though the circuits be designed as nonregenerativo circuits. The adjustment of each neutralising capacity is made experimentally by tuning in a very strong signal (IYA for instance), and then disconnecting the filament of the valve whoso capacity is to bo adjusted, but leaving the valve in its socket. If the neutralising capacity is not correct, the circuits on each side of the valve will have capacity coupling, which will transmit the signal. Ine neutralising capacity is then adjusted until the signal disappears. The neutrodyne is most effective when care is taken to have sharply-tuned radio frequency transformers, though tho adjustments required are more complicated if sharper tuning and greater selectivity are attained. There is no reradiation from the aerial of a neutrodyne receiver even when & regenerative circuit is employed in the detector valve, providiiig the set is correctly neutralised. Amplifier valves may be used throughout the neutrodyne. Don’t expect to get the best out of a neutrodyne if you use all k” of valves in it. Careful adjustments will be required. In faot. to attain the best results, it wants neutralising for each change of valve, even though you replace a burntout valve with one of tho same make. Of course, this neutralising is best left alone if you know very little ot radio, and you are getting results; and again some sets have their neutralising condensers bo built that .they are sealed and adjusted. In the writer’s opinion this is all right for a novice, who is very apt to take a liking to screw or unscrew all things when he looks his set over, but such a set that has provision for readjustments of these condensers is very nice.

The possibilities of wireless appear to be illimitable (reports our Sydney correspondent). A few days ago a programme was broadcasted from the bottom of a colliery. 3000 ft under Sydney Harbour. Now Mr Laurence Halbert has transmitted for listeners-in a graphic description of his emotions, from an altitude of 10,000 ft in an aeroplane piloted by one of the Commonwealth Government’s airmen. It is claimed that this is not only the first occasion on which broadcasting from an aeroplane has been successfully carried out in Australia, but that a world s record was established by transmitting at a height of 10,000 ft. The messages were sent out by means of an aerial 150 ft long, and suspended by weights from the aeroplane.