THE WIRELESS WORLD.

Otago Daily Times, Issue 20075, 16 April 1927, Page 2

THE WIRELESS WORLD.

NEWS AND NOTES. Bj Maona 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. ANSWERS TO CORRESPONDENTS. B. S. J. (Oamaru). —It is not necessary to have a separate lead-in wire soldered to the aerial. It is far better to use a straight, unbroken wire. A correspondent who adopts “Stuck” as his nom-do-plume, asks how long two .60 volt B batenes and one 4.5 volt A battegy should last, using two Phillips A. 306 and one 8.406 valves three hours per day every day in the week. —With the ordinary type of dry batteries, the B batteries should last about four to five months on a threevalve set. I should not imagine, however. that the beet results would be obtained from a dry A battery in conjunction with 8.406 valves. A small four volt accumulator should be more economical. From Gore comes an inquiry as to the beat aerial for everyday use. —This is a broad question as different wireless enthusiasts i have different views on the subject. However, I would suggest using a single wire, inverted L or T. about 120 ft long, including the down lead. There should be a short, well-soldered earth connection About 40 to 45 feet is a suitable height for most purposes. The down lead should be . kept as short as possible, and it should be remembered that when a T aerial is employed, the down lead should be taken from the exact centre of the horizontal wire between the insulators; this is very important. Amateur (Timaru). —Valves CX 301 A and UX 201 A are identical in every particular. The former is manufactured by the makers mainly for their own use. and UX 201 A is the export type. This type of valvcg is eminently suitable for an eight-valve spt. A TELEPHONE HINT. Many sets are marked with “positive” and ••negative” on the telephone terminals, but if your set is not so marked, look inside and see which of tho two telephone terminals is connected directly to tho hightension positive. The one which is so con neoted is the positive telephone terminal, and your positive telephone terminal tag should always be connected to this point This is not a fad, as so many might think but is due to the fact that, if your telephones are properly connected the steady plate current continually passing through them will add to the permanent magentism of the telephones themselves, whereas, if they are wrongly connected, this current may tend to steadily demagnetise your ’phones, reducing their sensitivity considerably. Telephones which have been dropped frequently are far loss sensitive than those which have been property kept. The reason for this is that any jolt or jar tends to upset their magnetism. CORRECT POSITION OF TUNING. The success or failure of a radio receiver often depends on tho position of one bun ing coil with respect to another (says Mr C. Slade in tho Sydney Daily Telegraph) Tho farther tho two coils are placed from each other tho loss is both the capacity and magnetic coupling between them. Also, when the two coils are placed approxi mately at right angles the magnetic coup ling is less than when tho two coils are parallel. The capacity of clcctric-static coupling does not depend to any gerat extent on tho relative angular positions of tho coils, but this coupling has an effect on tho effective right angle arrangement. It is always possible at one frequency to place the two coils so that tho sum of tho capacity and the magnetic coupling are zero. But thi s does not mean that a position can bo found where tho total coupling is zero. There is nearly always a residual coupling which is due to resistance common to tho two coils. But when the coils have been placed so that the sum of the mag notic and the capacity coupling is zero, tho residual coupling is usually very small, and therefore the minimum coupling between the two coils is also very small Tiro two coils are usually not quite at right angles when the coupling is zero, because tho capacity coupling distorts tho symmetrical arrangement. It is usu ally necessary to tilt one of the tho coils with respect to the other, or to raise or lowor it. When first placing the coils tho axis of the two should bo at right angles, and the plane in which tho axis of one lies and to which the axis of the other is perpendiuolar should pass through the middle of tho second coil. In other words, tho geometric centres of the two coils should lie in one plane, to which one axis is perpendicular and in which the other axis lies. This holds for either of tho coils with respect to the other, so that in reality it is necessary to line up two planes at right angles to each other. When tnis arrangement has been effected tho zero coupling position will be found by moving or tilting very slightly one coil with respect to tho other. An experimental way of finding the position of zero coupling is as follows; Connect the antenna and ground, or the output of an oscillator to the first ooil. Connect the other to tho grid circuit of an amplifier-detector circuit. Listen-in with a head-set. Then arrange the two coils until the signal that gets through is the least. It will bo found that the position is quite critical, particularly when the two coils are too close together. This adjustment is very important when building an RF set which is to be squeal-proof on the lowor waves. The adjustment should be made in every noutrodync, because without it the circuit will not neutralise. ADVERTISING BROADCASTING. Considerable attention has been directed of late to tho co-operative aspect of broadcasting, us it is becoming more and more apparent every day, that to popularise radio, others as well as the Broadcasting Company must assist in selling any commodity, and the parties concerned must interest the prospective purchasers or users in tho commodity offered for sale or use. It is thus very obvious that the battle ot publicity must bo taken into distant parts—the public must be told more and more about the advantages of broadcasting. It is not sufficient merely to broadcast and to display receiving equipment in shop windows ; the general public must be convinced that broadcasting is a good thing to have. For it certainly is a good thing to possess the means whereby music, song, and story may be brought into tho homo. And it is because so many people are unaware of tho opportunities they are missing that there are not more listeners. The part to bo played in developing broadcasting by the wireless traders is all important The success of their busmen and of broadcasting generally largely depends on the activities of wireless traders. They are in closest touch with the public; it is to them that tho sceptics and initiates come for information, and a great deal depends on the manner in which the trader treats them. Unfortunately it is probable that some prospective radio enthusiats have their initial enthusiasms damped by tho casual and careless manner in which inquiries regarding receiver troubles are answered. Even with satisfactory and obliging attention by traders’ assistants, tho great opportunities for extending the business are not grasped. It is not sufficient just to sell a set; the wise trader will endeavour to ensure that tho purchaser obtains satisfaction from it and that his interest in broadcasting is active enough to influence other purchasers. The element of service should never be lost sight of. Once again let us say broadcasting is a co-operative affair and the traders, if they are wise, must keep in close touch with tho users of tho service. Boardcasting service stations for attending to batteries, sots, etc. may not be as necessary as automobile service stations; but they certainly will bo wanted. Such a service is needed now in every city. Dealers individually endeavour to provide such service, but the attempts are not sufficient and arc not co-ordinated. 00-ordination of dealers’ activities will benefit dealers and listeners alike and is calculated to benefit the trade in no inconsiderable way. Further remarks on the above subject will bo made in next week’s notes. A receiver is not complete without a SF ERA VOX. Ask your dealer to demonstrate one to you. It combines sensitivity and volume with a handsome appearance being built in silver colour, and makes a beautiful contrast in any room. £5 ss, off all leading radio dealers.—N.Z. Reps., Brown and Bureau (Ltd.), Wcl-