THE WIRELESS WORLD.

Otago Daily Times, Issue 21241, 23 January 1931, Page 5

THE WIRELESS WORLD.

NEWS AND NOTES. By Magna Vox. Items of iooal interest are invited by “Magna Vox J ' 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. Metres. 7ZL, Hobart 535 3AR, Melbourne 484 4YA, Dunedin 463 2FC, Sydney 442 2YA, Wellington 420 4QG, Brisbane 385 3LO, Melbourne 371 2AB, Sydney 316 2KY, Sydney .. .. .. 280 ANSWERS TO CORRESPONDENTS. “Voltage,” Clyde.—l should say that the trouble is due to your resting the speaker on the cabinet. Take it a good distance away from the cabinet, and be sure that the cord does not come in- contact with any part of the set, especially the detector valve. Fit a spring socket to your detector valve, and it' would also be an advantage to rest the cabinet on a sheet of rubber or some fairly resilient substance. Write again if this is not successful. “ Abey,” Milton. —Probably your set is not neutralised. Remove any fixed or variable condensers in series with the aerial, then tune in a station in the centre of the dial. Remove the first R.F. valve and insulate one of the prongs with a piece of paper. Replace the valve, then adjust the neutralising condenser until the station almost fades away. Remove the insulation from the valve prong and replace the valve, when the station should be heard at good volume. Treat each R.F. stage the same. “ Coupler/' Dunedin. —It depends largely on your requirements. The advantage of a transformer coupling is that transformers have a greater amplification per stage than resistance coupling. It takes three stages of resistance coupling to give the same output as two transformer stages. Resistance coupling generally gives very little distortion. In case of trouble with the stage, it is an easy matter to replace one of the resistances, but in the case of a burnt-out transformer winding, it is necessary to replace the transformer. CLOSING OF B STATIONS. The fact that three of the local B stations are now off the air, as a result of the ultimatum issued by the Australian Performing Right Association, appears to have come as somewhat of a blow to listeners generally, notwithstanding that the full position has been a matter of common knowledge for some months past. It would appear that license holders have been optimistic enough to believe that the association was merely “ bluffing,” and that it would not enforce the payment of its just dues. Possibly there were some grounds for such an assumption, and yet, now that the position has come to a head, no one can deny that the association has acted perfectly within its rights, and that, after all is said and done, it has offered to meet the B station owners on a very reasonable basis. The early demands of the association were certainly more than the ninor stations «ould cope with, but later, t modified these to a request for a paytent of £2OO ir settlement of royalty fees fom the 23 B stations in the Dominion. A this works out at less than £lO per slition per annum the charge could not be said to be in any way exorbitant,, and it : seemg strange that the enthusiastic bad of amateurs who control the statics could, not devise some means of meting the charge. Of course, no one rcaises better than the writer that the listqers should pay for the service they receive from the B stations, but after all, they are already paying 30s per nnum, and many of them, maintain (prohbly with some justification) that some arrangement should be come to wherby the B stations should receive a propdtion of the amount. A solution of theproblem now appears to rest with the liteners themselves. The closing of the stations will leave a sad gap in the aeial programmes, and their nightly transmssions will be missed by every license holder who appreciates satisfying entertanment of a particularly high standar. A listeners’ league—an. prganisatin for coping with a position such as he present one—has been founded, but witbut members it can do little. It therefor behoves listeners-in to rally round tie league and so strengthen its position :ha± it will be in a position to take deflate action. . In fainess to the proprietors of the amateur tations, it should be noted that a numbe: of them were quite willing to pay thei proportionate share of the amount aked by the l Performing Right Associate, but quite rightly they wanted some guauntee that this payment would be strict!; without prejudice and would not be tsen as an admission of their liability i the future. As a matter of fact, a bare firm of music-dealers in the city offers some time ago to pay over one statiofs proportion, but the licensee refused to agree to this as, had he done so, he word immediately have admitted liability iuhis name. DIRKTIONAL SPEAKERS. The majo-ity of cone loud-speakers are very deciddlj directional, and not only do they siuid loudest when you are directly facng them, but they also sound better. Ths is a point to bear in mind when you mite a friend to listen to your results Do not arrange the loudspeaker on line table alongside the set and. let yojr visitor stand near the receiver. Povide him with a chair which is so placed that he will look right into the cone, aid have the speaker at about the same bight from the floor as the head will b. Also, do not put him too near to theloud-speaker, but let him be at least twoor three yards away. These may be smd points, but you have only to try listning in different relative positions to the loud-speaker yourself to appreciate feeir importance. A NIVEL BROADCAST. When Mis Mercedes Gleitze, the celebrated Engish long-distance swimmer, sets out eary next month on an attempt to swim acoss Cook Strait radio set owners in lew Zealand and in Wellington particulrly will have an opportunity of followingher progress. Arrangements have been ompleted with Miss Gleitze, Mr J. Tait,whose launch will accompany the swimmer and station 2YA by Messrs Green and )ixon, two Wellington radio enthusiasts, rho for several years have had consideiible experience in amateur transmitting. Their call signs, ZL2GR and ZL2BO espectively, have at various times been bard in all quarters of the globe. The pparatus which they intend employing is a portable short-wave telephonic tranmitter using the Heising system of mdulation. The wave-length will be abomSO metres. Power will be supplied fron heavy-duty dry batteries. The set will b sheltered from-the weather in a cabin ii the bow of the boat, and the microphoc will be so arranged as to be, able to e carried about within a radius of six or seven feet. For some time the trasmitter has been on test and has give) every satisfaction, having been heard al over New Zealand. Dur-

ing the trip across the strait the apparatus will fc working all the time, and at intervals tfe messages will be rebroadeast from 2YL For reception purposes an ordinary troadcast set will also be carried. Anther mast will be temporarily erectd on the launch to support an aerial. Tlephony, Mr Green stated, has never boo used for a similar event in New Zealnd before. Wireless was employed a fcv years ago in a yacht race, but in that cse the Morse code was used. He advised a many people as possible to listen-in o: the short-wave length, as that would be more satisfactory that the rebroadcast o" a longer wave-length. A SIM’LE WAVE TRAP. Since the iauguration of the Regional scheme in Bgland a large number of rejector wavetraps have been designed. For the horn-constructor the following simple and iexpensive “ P,W.” Brookman’s rejecto should prove satisfactory. The device 3 claimed to eliminate a powerful loca station and at the same time to give excellent distant reception. The rejector e constructed and operated as follows:—;irst obtain a piece of tubing of some pod insulating materia] 3in in diameter nd 2Jin long. In one end of this fit tvo small terminals (about fin from the -nd) and cut a wooden crosspiece to fit neatly across inside the former, Thi crosspiece can be of wood

about Jin square section and is secured in the tube by means of a small screw passing into each end through a. hole bored in the wall of the tube. It is to be placed at the eame end of the tube as the terminals. First screw to its underside a fixed condenser of .001 mfd. capacity and to its upper aide a compression type adjustable condenser of .001 mfd. maximum capacity. Put this side apart and proceed to wind 45 turns of No. 24 D.C.C. wire (or 42 turns of No. 24 D.S.C.) on the tube in a single layer, starting about 3-16 in from the Snd opposite the end one with the terminals. Leave a few inches of wire at start and finish sticking through holes in the tube for connections (a 2oz reel of wire will be ample). Now fix the crosspiece in position and wire up thus: Upper end of coil to one terminal and one side of compression condenser; other side of compression condenser to other terminal and one side of fixed condenser; other side of fixed condenser to remaining end of coil. Connect the aerial to the second terminal and wire the other to “ A ” on the set. Very carefully adjust the compression condenser until you find the point at which the local station suddenly and rapidly diminishes in strength and even vanishes (unless the set is very powerful it will do so). Check the point by noting that a variation either way lets the local station thrpugh again, locate the exact rejection setting as accurately as possible and then tighten the locking nut under the condenser knob. The local station will then be cut out. POWER DETECTORS. A good deal has been heard recently about power detection, and a certain mystery seems to surround what is often considered an entirely new method of rectifying H.F. Actually there is nothing particularly unique about the scheme. Strictly speaking, any detector valve which will handle a tfery large radio-fre-quency input, and is capable of giving a considerable power output, is a power’detector. The valve may work on either of the two common forms of rectification—namely, leaky-grid condenser or anode bend. In order to get a’ high magnification in a power detector, and also to obtain a large grid-volts base, a high value of H.i. is employed. It is also usual to employ a low impedance valve so as to be that a large grid-owing can be handled without distortion. It is sometimes assumed that it is from the_ latter fact that the name of “ power detection is obtained. In reality the term originated in an altogether different way. This type of detection was first used in loud-speaker sets with only one L.F. stage, and because there was only one audio amplifier (the output power valve) it was necessary tor the detector valve to have a large output. Otherwise the power valve would not have been properly loaded up. The expression “ power detection ” was thus applied to a detector valve with sufficient output to load up the power valve. Power detection is most useful when powerful xlJc. stages are used and great volume desired. Particularly does this: apply where local station working .is concerned. One of its chief drawbacks is a difficulty of obtaining a • smooth reaction contro with it.