THE WIRELESS WORLD.

Otago Daily Times, Issue 21033, 23 May 1930, Page 5

THE WIRELESS WORLD.

NEWS AND NOTES. By Magna Vox. » J} ems ‘ °f, local interest are invited by Magna \ ox ” for publication in this column. It is necessary that such matter should reach this office by Tuesday of each week for insertion on the followma Friday. -rrr r T , Metres. iZL, Hobart 535 3AR. Melbourne ... .. .. 434 4YA. Dunedin 463 2FC. Sydney 442 2YA. Wellington 420 4QG, Brisbane 385 3LO, Melbourne 371 2AB. Sydney 316 2KY. Sydney .. 280 - ANSWERS TO CORRESPONDENTS. R. F. M., Dunedin.— Your trouble ’ is caused by microphonic valves, 1 See that the valves are in shock absorber sockets. Place the cabinet on corner pads of sponge rubber, and sponge rubber under the speaker also. I should not advise you to have your speaker op top of the set, for. although microphonic noises may not always be prevalent, the vibration is detrimental to the valves. “Magnet," Dunedin.— (1) I am afraid I cannot help you. The dealer' from whom you purchased the set is the only one who could shed any light on the matter. (2) Any reputable electrical supply firm should be able to supply your requirements at a very moderate cost. (3) A metre is ap- • proximately 40 inches. To correct metres into feet, multiply by 40 and it divide by 12. ‘Howler,” Lawrence.—Assuming that you ar ? us * n 2 a 4-volt accumulator, your valve has probably lost its emission. If you are using an r.f. choke in series with the piste of the detector valv e. try shortin* it out. Try also a .002 fixed condenser across the secondary , of the transformer. If this does not stop the oscillations, reduce the number of turns on the reaction coil by about eight, or change t ll?„„ react * on condenser for one 0! .00025 m.f.d. W. M‘G.. Dunedin.—Try reversing the ; condenser connections. If two different types of transformer are used, try reversing the primary winding connections of one of them. Also try a .002 fixed condenser across the secondary of the first transformer and a 100,000 ohm variable resistance across the secondary of the last transformer. See that the plate and grid wires are well ’separated and that they do not run parallel with each other tor any appreciable distance. WIRELESS TELEPHONY. . ~ Yet another success has been added to tne dong list of radio marvels of recent months. • A short time ago Marconi, the discoverer of wireless, from his . yacht Llfetra in the Mediterranean, switched on f ® I?sLts of the electrical and radio exhilntion at the Sydney. Town Hall. On Apnl.3o last the Prime Minister of Great Britain Mr Ramsay MacDonald, and the Prime Minister of Australia. Mr James ocullin, came into personal contact over the ether, by the first .world telephone conversation between two Prime Ministers in the British Empire, who were separated by a distance of 12,000 miles. Ihe voice of Mr Ramsay MacDonald was as clear as if he were speaking only a effort distance from the P.M.G.’s room - at Canberra, where Mr Scullin was located, hearing; ms brother Prime Minister’ converse with him over thousands of .miles of land and water. .The conversation ’ between the’two Prime Ministers. was broadcast through Australia by the Australian Broadcasting Company’s chain of “A” class stations. It was a conversation that lent an added fillip to the Australian dinner hour. On the other side of the world, it was morning—breakfast time, a , n . thousands of British listeners had tneir breakfast hour enlivened by the cou«^l a ii oll i °l ,^ le T own Prime Minister with that of the Australian Prime Minisccr, 1 hey, too, were as awestruck at the wonders of radio as their Australian brothers. Wireless telepnony is as yet W infancy. The advancement of science i f- ra P K i ln this direction, and in a short fame telephonic’;conimunications will he indulged , in hetweeh Australia and ’ OT’ 4 0I T- er ‘ globe. The .Charge,' too, will dimmish as the demand becomes popular, and the time is not far distant when telephonic communication between f. U r 6 A ra l la +i, and Zealand and other parts of the world will be no more expensive than a trunk call between Christchurch and Dunedin. With the introductelephony, linking the outposts* of the British Empire with the Mother Country, the 'twentieth century Ago"* 0 do ' Vn m histor y as,“The Radio CONDENSER TROUBLES. _ In ■ high-powered transmission on Jong th c e aer i' a .l tuning condensers i« e ? en f a,1 y °f the oil-filled type whilst in short , wave transmission air is used as the dielectric. In both cases very high voltages may be involved, so that great care is necessary to avoid breakdown. h or instance, the pressure of stray mires in the oil dielectric may easily lead , Tlle effect, of the electrostat.c field is to draiy out the fibres i,„ B w 1Se ’ so i , caus ' l1 B them to bridge the gap between the plates. In the air-filled type of condenser, a small surface rough°S e ° f *1?? p!?tes may start a brush discharge which in turn will cause, .arcing at a comparatively low voltage. RADIO LITIGATION. in'pw!? have recently been two lawsuits in I lance, both concerned with broadcast reception, the verdicts in which have considerable satisfaction to hsteners m general. In the first case the plaintiff was a doctor who possessed a wireless'receiver-which the exto be of good, careful and scmtifio construction; the defendant was a ® af f proprietor, possessing an electrical gramophone used for dancing, which experts blamed as the cause of the disturbances. The itfotor attached to this machine, however, could be replaced by a silent piew of mechanism which would cause no disturbance. The cafe proprietor was compelled, under a penalty of 50 trancs a day for a month, to cause the mterterence to cease and also to pay 500 trancs damages to the doctor. If mav be mentioned that France has no officia/service to search for the cause of electrical interference and to compel those causing it to take steps to prevent such annoy-, ances. in the, second case, a tenant of Nancy who, as the result of an action Drought against him by his landlord, had been ordered to pay damages and to for- ■ • Jr Wl , re ess »et for troubling his neighbour, has succeeded in having the judgment upset and transferring the liability for damages from himself to the landlord This extraordinary result was produced, apparently, by the evidence of the neighbours, who stated that, far from being annoyed by the music proceeding trom the loud speaker, they were, on the contrary, charmed with it! TESTING FOR FAULTS. It may so happen that when vou have tuned in your set in the usual manner no signals are heard. The first thing to look at 111 this case is the aerial. If it is an outdoor one it may have fallen down or you may have forgotten to attach the lead-in to your set. Having seen lo the aerial the next thing to do is to see if the earth wire is connected and making good contact to earth. The aerial and earth being both 0.K., you have localised .the fault to your receiving set. The next test is to make sure that the windings of the magnets are not burned out. A good and reliable test is to put earphones on in the usual manner and hold one terminal tag and rub it against a piece of metal a key will do. If the phones are m good order you will hear a weak but distinct scratching sound in them, corresponding with the rubbing. This sound is due to the minute galvanic currents set up by your own body, and only a very sensitive electrical instrument would respond to such tiny currents. The batteries should next be tested by means of a voltmeter to see if they are giving a correct voltage. Th 6 different components in the set itself should now he tested. A pair of phones, a small flashlamp bulb, and battery will be very use fill for this purpose. When a small battery of four volts or so is connected directly to a flashlamp bulb the latter lights up brightly, but if the complete circuit is broken, or has’ a high resistance brought into series with it. the little bulb will not light at all. A resistance of a few ohms such ns that which normally exists in an ordinary plug-in - coil will cause the light in the bulb to become dim. You can make up a simple tester on these linos by fixing a flashlamp bulb-holder to a piece of wood with a terminal at each

®. n< k X ou should join one terminal of the battery to one terminal of the flashlamp. One loose lead should be joined to the battery. The ends of these two .eads can now be brought across any of those points it is desired to test for continuity of. circuit. You cannot test any-r thing inlying a high resistance with this tester, such as a pair of telephones or an , . transformer. You should use this device lor testing soldered connections,-, plug-m coils, flexible leads, and their contacts, and anything of a low-resistance, • i.e., not much wire in it. A variable condenser can be used for shortening vanes f’ rlr ‘K ln ,K the leads across its terminals. It the bulb lights up when tin? vanes of the condenser arc rotated, then these must be touching and should be put right. Make sure that there is no other path, such as a coil connected across the condenser, by which the current can pass, otherwise the bulb will light up and give a wrong inference. It is best to disconnect the component to be tested; then; there 19 no possibility of an alternative* ; path being offered. The following are some of the tests which can he carried out by means of the bulb tester. Spring ! contacts in switches, grid leak, and other such holders should be tested bv holding the tester leads firmly against the metal parts forming the contacts. Leads and terminal connections can be tested for continuity of circuit. Faulty connections wi I be indicated by a dim light or no light at all. Variable condensers can be tested for scraping vanes or other causes ot short circuiting, such as pieces of solder or tiny pieces of wire lodged between the vanes. Coils can be tested for continuity. The connections between variometer terminals and their moving coils can be tested, also the windings for continuity. When the two leads are held across the terminals of a fixed condenser no light should result unless the condenser is faulty and has developed shortcircuit High-frequency transformers can also be tested for continuity and shortcircuit between the windings.