THE WIRELESS WORLD.

Otago Daily Times, Issue 19066, 11 January 1924, Page 2

THE WIRELESS WORLD.

NEWS AND NOTES. (By Magna ' Vox.i [ltems ’of news, comment, suggestions, etc., will be welcomed by “ Magna Vox.”] Owing to tbe fact that Beath’s Orchestra was unable to put in gn appearance on Wednesday evening an ' improvised programme was broadcasted by 4 VA. Messrs R. and V. Robinson were the operators. Gramophone and Player piano items were broadcasted, Messrs 11. and G. Death gave violin and piccolo items, Miss G. providing the accompaniments. Miss P. Stewart and A. Claridgo gave songs. A programme has been arranged for to-morrow evening's concert. Wireless telegraphy is a wonderful thing for getting people out of difficulties. A doctor had driven to Boston with his wife to see her off on a steamer bound for New York. Ho performed the seeing off so well that ho saw himself off as well as his bis wife, for when ho hade the last tender farewell he came on deck to find the gang plank raised and the dock a hundred yards away. He had no oilier choice but to continue the vovage, as the captain refused to turn back; hut, not seeing why he should lose his oar, he got the wireless operator to send a message to the Heston police, ft was luckily picked up by an amateur, who promptly no(ified the police, who proceded to carry out instructions in a satisfactory manner. The ear was berthed in a garage, where the doctor recovered it sonic considerable time later. To test the effectiveness of radio for the purpose <•( (racking criminal- an in((nesting ex', i rimer-, was recc-d-- carried out by the dish Broadcasting Company. The broadcasting station at. M a peers House. 21,0. announced that the ‘‘criminals” had escaped from 2T.0 in Daimler and H.S.A. cars, the cars having been sent over previously selected routes with instructions to go fairly slowly through towns and villages. Five minutes after the start the first car was hailed and received the thumbs-up signal showing that it had been identified. At each centre of habitation numbers of listeners were waiting, and it is suggested that had the chase been in earnest the car would have pot no further than the city, for it seemed that half the inhabitants had come out in response to the appeal. The car was haiFd by sol •fury listeners in the most unexpected and out-of-the-way places. At Haldcock, one gentleman had taken the hunt seriously and followed the car for -many, miles before he was shaken off at a by-road. The experiment was a distinct success, and shows another of the possible services of radio to the police. Accounts of such services, however, fail to indicate that radio might 5 prove of much service to the criminal also./ One of the most tronbesome effects with a valve receiving set, especially noticeable with weak long distance signals, is that due to “body capacity.” It manifests itself when endeavouring to tune in weak C.W.. as, with the hand on or near one of the tuning dials, the signal is picked up hut immediately disappears on removal of the hand owing to the fact that the extra capacity in the set, caused by the capacity of the human body to earth, has been removed with a consequent change in the wave-length to which the set is tuned. There are two methods of avoiding it.- The first is to shield the parts of the tuning set by placing a metal sheet (tinfoil does quite well) at the back of the panel, the instrument being insulated from it. The metal sheet should he connected to the earth terminal. A similar effect would he gained much more cheaply by mounting all the parts on ebonite bushings in a metal (not ironl panel. The second and better way is to so connect in the instruments that the rotating part to which the dials are connected are at earth potential, or at earth potential so far as the radio frequency currents are concerned. For example, in the aerial-earth circuit the moving plates of the variable condenser should bo the earth connected ones. In the tuning circuit, where the effect will give most trouble, the fixed plates should be grid connected and the moving plates to the filament battery BONG-DISTANCE RECEPTION. Mr T. S. Macdonald, 4AH, Waiwera South, who claims a world’s record for the reception of American amateur radio stations by logging no fewer than 62 different stations in one evening, has had further successes. On Sunday night last ho logged 6XD, Oakland, California, using a detector alone. With one to two stages of audio frequency speech and music could be heard clearly six feet from the three ’phones which were used, and the carrier wave could be heard loudly all over the room The Californian station was as loud as, and much clearer than, any New Zealand station which Mr Macdonald has picked up. Nine complete ilems were received, consisting of violin and band pieces and pianoforte items. At 0.24 a.m. (New Zealand time) the following announcement was heard:—“6XD, Oakland, California, signing off at 4.55 a.m. (American time). Good morning.” On the same night Mr Macdonald logged about 50 American amateurs. For 12 nights listening in Mr Macdonald logged 278 different American amateurs, representing every district in U.S.A. Of this number, 154 were sixtli district amateurs. The sot used was a three-circuit tuner with two turns of the primary coupled to the secondary, and a loading- coil in series with the two turns and a tickler coil coupled to the secondary. WIRELESS TERMS. Earth. —An essential part of an aerial system. Such a system consists of two parts, tbe aerial wire and the earth wire, the two forming a condenser (to be defined later), which is charged (in the case of a transmitting station) to a high voltage in order to set in motion waves in the ether, and, in the case of a receiving station, receive the waves. The earth usually consists of a network of wires or metal plates buried in the earth and connected together. In the case of an amateur station, a suitable earth may be obtained by connection to a water-pipe or an earth pin driven in the ground. On ships use is made of the iron hull of the vessel. Primary.—That part of a loose coupler which contains the thicker wire. It is usually the outside tube and is directly connected to the aerial, earth, variable condenser, and in some valve receiving circuits to the grid of the valve. It is made variable by means of a slider or switch. The term also refers to the input winding of transformers, induction coils, and similar instruments. The gauge of wire used for the primary winding depends upon the gauge to be used for “the seondary and the purpose the instrument is to serve. Secondary.—The inner wire-wound tube that slides inside the primary of a loose coupler. It is usually wound with finer wire, and has a switch fitted at the end. It is connected hi the crystal and telephone circuit of a, crystal receiver, and is used as a reaction coil in some simple valve circuits. Ihe term also refers to the output winding of transformers, induction coils, etc. Sometimes the windings of primary and secondary are very close together, at others they are a considerable distance apart. An instance of the former is the modern highfrequency transformer used in wireless, where both windings are wound together. In referring to the ratio of transformers, the terms 1 to 5 or x to 10 are used, indicating that the. secondary has 5 turns to 1 of the primary or 10 to 1 as the ca.se may be. Loose Coupler.—A type of tuning cod very popular wif.li amateurs, aiul 0110 of the most efficient for general use. It employs the principle of mutual induction, jwo coils arc used, one capable of sliding ins de the other, thus making the coupling, or the degree of proximity of one coil _to the other, variable. Owing to the induction effect between (he two coils good selectivity of tuning is attainable. Capacity.—The property which a condenser has of receiving and holding a charge of electricity. Capacity is determined by the size of the plates, the distance between such plates, and the nature of the substance filling (ho space between the plates (the dielectric). It is calculated by a formula based in these factors. Roughly, capacity is the electrical value of a condenser, the iorm is also used to indicate the total output from an accumulator or primary cell. Inductance.—The property a conductor has tendin'* to prevent the starting, stopping, or variation of the flow of an electric current in it. This property is greatly increased when the conductor or wire is in the form of a coil. The moment a current starts to flow a magnetic field is created round the wire, which induces a current in the opposite direction to that which has commenced to flow. This induced current momentarily obstructs the real current, which obstruction. however, is quickly broken down. This induced current is caUed “back” E.M.F. . (Electro-motive Force) The same effect is caused by the stopping of the current, the induced current lending to maintain the flow.