WIRELESS NOTES

Evening Star, Issue 19143, 9 January 1926, Page 3

WIRELESS NOTES

SHORT WAVES [By Electron.] Latterly our papers have had many paragraphs recording the development of short-wave transmission, especially in conjunctiion with the beam system, and I propose to give you a popular explanation of what is going on. Suppose you imagine a wireless wave ns a wave on tho sTfrTa-cc of a pond of water, and further imagine a succession ol these waves' following one alter the other. These waves may follow one another at very short distances (say, a low indies from crest to crest), or they may ho at a greater interval of a foot or more. The only way to distinguish hetwoe.n two such typos is to stale the wave length or the distance from crest to crest. 11 the various waves all travel at the same velocity (as wireless waves do), (lion it will ho understood that the shorter the wave length or size of wave the quicker will it require to vibrato nr undulate to _ travel a given distance m the same time as the longer wave. It should now he grasped that wave length and rate oi vibration are interchangeable tonus, and when we speak of a •Ttri-nic4.ro wireless wave wo mean not only a wave that follows at a distance of TOO metres from tho previous wave, hut also a wave that is vibrating with a frequency of ],000,000 vibrations per second, the rate of propagation of wireless waves being approximately TOO,OOO,UUO moires per second. When wo speak of a short wave we moan ono having a wave length ol under 50 metres, which is the same as a frequency of (i,000,1)00 vibrations per second. This is a stupendous rate tor anything to vibrato at, and in radio work it becomes extremely diflicult '.o handle the transmitting power when a reaches such a high frequency. In fact, only a few years ago it was considered too hig a proposition to handle successfully, and as a result all the highpower radio stations used waves \uth a much slower and sedate rate of vibration; the higher the power used 'lm slower the frequency chosen. This wont on from year to year, tho *.izc of tho stations increasing Iron) one or two horse-power to 1 .TOO aorso-pmvi r and more, all the time the wave lengths being chosen so that the frequency would lie com pant lively low and easily handled. Finally a sl-agc was reached where the frequencies began i( over. la/Tand interfere with one anoili.w, and radio engineers could see ih.ir m a short time all tho available channels of communication would he used mi, an international confusion would be inevitable. TI.US AM ATEI'IFS ASSISTANCE.

It was at this stage that. a new I factor entered the held of radio acxeii opmont. For a few years radio experimenters throughout the world had been finding that, using the short waves of high frequency I hey wore Inrced by law to adopt, they could, obtain surprising results, and at times could accomplish transmissions over distances t.hat even vbo high-power stations could not equal. As time, went on and I hey adopted shorter and shorter wave lengths it, become obvious that the shorter the wave length the farther it seemed to travel, and at la<t, communication from otie side, of the world to ihe other was established using ve.ry little power, but with extremely short waves. New Zealand amateurs were to the fore, in these epochmaking discoveries, and even to-day are aec.omI pushing daily feats in long-distance, transmission that arc hard to equal. As an instance of what is being done, Air R. Slade (radio tA(D, will: a, short length of ware hung from a mas), above his bedroom window, can establish communication with almost any coyntrv in the world night or day, and with a power no greater than that used by an electric iron. He uses a wave length of 20 metres (10.000,000 cycles!), and it is only by the use of t'liis extremely short wave length t.hat. (hose results can he obtained. Were he to use a wave length of 1,000 metres or so he would find it difficult to communicate with even Australia, our next door radio neighbor. Of course, the ultra high-frequency r went has taken a great deal of taming, and even now plays tricks that. 'He respectable 300. metro current would river dream of. For instance, with the I-;'-metre current a slight overload or faulty adjustment and the glass of the valve will shatter to pieces. It does not melt or fuse,, simply seems to shatter, and extreme care is required with every piece, of insulation; otherwise spectacular results may follow. 4A(i is not the only a'"aieur doing, this work; there arc others even in Dunedin obtaining equally wonderful results, but .1 mention him as an example. COMMERCIAL RADIO. Naturally it did not require much time before ih,<> commercial radio engineers realised the possibilities of the very short waves, and as a result we have to-day at least seven of the

world’s greatest radio stations using wave lengths from 20 metres to 83 metres for their regular communication with one another, and more stations aro being rapidly equipped for the new system. Tho important point is that while with the long waves enormous towers, heavy and costly plant, arid tremendous powers are required, with tho short waves the whole plantis very small and insignificant compared with the big plant, and costs only a., fraction of the super station, yet ao-i eoiiiplishing the same, or even more,, work. Jn a few years we will find that' short-wave transmission has almost entirely supplanted the long-wave system,and when this happens I am afraid that our amateurs will bo_ even mow restricted in their experiments than! they arc at present. The only Roln-| thin is for the keen experimenter torj work down to the ultra-short waves be-> ; low 20 metres, and it would bo hard to[ predict what astounding results mightrl be obtained in this band. | RADIO VLD.NN

Last Saturday 1 connected up valve lion-regenerative set (30-ium .00025 mfd condenser, and 201 A valve*' with the acrid and earth cormeoted, straight on to the coil and A by-pass condenser was also used) across the phones and R battery. WiUiJ this sot eight miles out of town I wasi agreeably surprised with the darityn and volume from VLDN. 1 don’t sug-t gesl- (.bat they wore loud, but at theJ same time most of the transmission 1 could be followed with lwo_ pairs of phonos, tho softer passages being rather laini to distinguish. A great deal of ' the “ mush ” t hat seems to be nnavotcH able with a regenerative set was ab-.j sent , and the programme was very | pleasant to listen to. Later on I added I a stage of audio with a 1/1 transformer. anti still without regeneration. With this set the reproduction was all that could he desired on the phonos, but not sufficiently loud to operate the speaker effectively. By adding; regeneration the volume was increased greatly, hut the quality .suffered severely'. ' This is a sure sign of too much spurious noise in the transmission, and a resistance across the modulator input) circuit .should eliminate some of the noise. Willi a perfect transmission the use nr otherwise of regeneration does not affect the quality to any extent, except where extreme regeneration on (he point of oscillation is used. For those who would have the best from VLDN* 1 suggest trying the non-re-generative valve set with audio amplification, and even il they have to use the phones they will find the quality very good indeed (except on the very loud passages), hi connection with tho last comment, it seems to me that more control of the modulation is required soft passages requiring more gain, ana louder passages less. Of course, this means an attendant with his eye on the microphone circuit ammeter ana, his hand on the gain control, and per-: Imps Ihe staff have quite enough to handle already; nevertheless, it would he a derided improvement. A NEW USK FOR, VALVES. Those vim witnessed the fireworks display at the Exhibition will he pleased' to hear that-, according to “ Reflex ” in, the ‘Soul bland Times.’ ft tile now R.C.A. power lubes can he made io .fit standard ‘nickels' by the use ot adaptor-." Ji is hard to imagine wlraS .further use remains to he discovered 1 - for the veratile valve.