Mainly about Construction

Radio Record, Volume I, Issue 1, 22 July 1927, Page 14

Mainly about Construction

BY

MEGOHM

Radio, with all its wonders of the moment, is still in its infancy. The past twenty-odd years’ have seen wonderful developments, but what is to. follow in the years to come makes it a thing of the future with a‘ wealth of wonderful development in store to be gradually unfolded. Television, more. wonderful than the wireless telephone, whereby we shall see distant scenes as we now hear distant music, will soon be a commercial proposition and an every-day delight. The youth of to-day will have seen many new and great inventions by the time he reaches the age of fifty, and those who make the effort to understand radio more or less thoroughly will have a life-long hobby of exceptional interest and continuous novelty.

The best adjunct to the reading of) good text-hooks on the theory of radio, is practical construction. ‘Thedry alone cannot give the knowledge acquired by combining it with practical work, and those who develop their constructive abilities will derive far greater satisfaction from logging distant .stations through the medium of a set of theit own. construction than by twisting the knobs of a bought set that they might never take the trouble to understand. Of course it is qnite admitted that not everybody is constructively inclined, or can spare the time for it, and that those who buy a set with the cne object. of being provided with musical entertainment will reap unlimited pizaure from their investment. Put thor who feel that construction alone w.11 satisfy their ambitions will gain im many ways by developing their craftsmanship. They will learn alongside the technicalitics of radio, the genecal principles «underlying all practical work-foresight, care and patience. Cabinet work, soldering, drilling, screwing and fitting together learnt in wireless work will often be turned to good account in other directions. A constructor naturally becomes more. or less of an experimenter, and as such his set is more frequently made up on a neat: board rather than in a cabinet, so that aiteratious and improvements van be easily made at any time, and such a set being roomy, often gives wetter resul:s than when componen:s are closely huddled together in a cabinet without careful experiment or ne- . vessary shielding. There ave cetvain accessories that an amateur casnot make, and valves, headphones, !cud-' speakers, low-tension accumulators and audio-transformers would so far as most people are concerned, come under this heading. But it is in the general design, lay-out, wiring-up, .switching attangements and operating convenience that the amateur has plenty of scope for ingenuity and inventiveness. And here it may be pointed out how very accommodating wireless construction is in suiting itself to the amatenr’s capabilities, as he is able to purchase ready-made any article that he does not fecl disposed to-make, though he miay’ aim to eventually make everything possible. The modest crystal set may be chosen as a first attempt at construction, and is not to be despised, at least as a heginning. To get really good crystal results is an achievement, and nothing will beat the solenoid coil wound with Substantial wire on the low-loss plan, that is, with a space between each turn equal to half the thickness of the wire Having erected a good ontside aerial, and obtained good ’phone results \,ith the crystal, the next step may be tne addit:on wf an andic-transformer aud valve to ar plify the output of she crystaJ, giving fair loud speaker volime if } close to a rein station, or two amplifying Vvaives te give good loud speaker valume under the same conditions. When a valve circuit has been tested and gives good results, the enthusiast may he pleased, but not satisfied-it will always he his aim to improve towards perfection. Then come the refining alterations, grid leak and fixed condenser valves are altered and results" tioted, positions of adjacent wires ad- | justed, different valyes may be tried,

high tension voltages varied and variable condensers testea to prove that they cover the required range. There is constant interest in making alterations, and noting results, and from this experience sound knowledge is obtained, All this work develops the virtue of patience, enabling otherwise tedious problems to be coolly dealt with and finally solved. Broadcast listening is uow of such importance that every effort should be made by set owners to suppress any tendency for howling and vscillation to radiate from their aerials, and as already advised in a circular just issued by the Post and ‘Telegraph Department, it will be well for purchasers or coustructors of valve setsmto consider nothing less than a two-valve outfit, the first valye to have a neutralised highfrequency arrangement to prevent radiation and consequent interference with | nearby receivers. ‘The second valve will of course be the detector, and one or two low-frequency amplifying valves. can at any time be added to these. If. it is desired to add a_ high-frequency stage, *then it may be necessary to sep-. arately .shield each of these stages and also the detector to prevent interaction. It is as tyvell to warn the beginner against wasting time on two and threecoil circuits, very much featured in certain imported tadio journals The two-coil circuit is illegal in New Zealand, and the three-coil, whilst more selective than the two-coil, can cause a great amount of interference in inex‘perienced bands and moreover, has been superseded in every way by circuits with an improved sy stem of aerial tuning and reaction coutrol. The superheteredyne is not a circuit to be recommended for home construction. It is eomplicated, and the saire ‘results can be obtained by newer circuits employing a less number of valves It is illegal to use a super-het. on an ontside aerial in New Zealand. The Browning-Drake and neutrodyiie cirenits are hoth, suited to home construction, presenting no great difficulty. The Browning-Drake, though neutralised, is a partieularly good circuit for search: ing ont distant stations, a well-con-stracted set with four valves having a range of about ten thoasand miles. Such a set, employing low-loss coils, is almost sa selective as a super-het. When buying components it is good to have the assistance of an experienced radio amateur, but in any case the main factor be "how good’’ and not "how cheap.’? This remark applies particularly to audio-transformers-caly purchase large-sized ones, as they give good tone and do not Gistort: the small patterns are out-of-date and will only give tinny tone and distorted music, and speech if carrying any volume, and owing to their fine windings, easily fail through burning out. No very imposing kit of tools is ne--cessaty for a beginner at_ construction, the main items comprising a hand-+ drill, cutting pliers, screwdriver, soldoering gear, aud a few ordinary carpen--ter’s tools, | Do not be satisfied with untidy-look-ing work: aim to produce something good, well designed, easy to use, neatly laid-out and arranged even if it is only on a hook-up board. Quality of work will soon improve with practice, and this will often assist to get better qual- | ity of reception.