THE WIRELESS WORLD

Otago Daily Times, Issue 23083, 8 January 1937, Page 2

THE WIRELESS WORLD

By Magna Vox

NEWS AND NOTES

Items of local interest are invited by " Magna Vox" for publication in this column. It is necessary that such matter should ■•each this office Dy Tuesday of each week for insertion on the following Friday 2BL, Sydney.—74o K.C., 405 metres. 2FC, Sydney.—6lo K.C., 492 metres. 3AR. Melbourne.—63o K.C.. 476 metres 3LO. Melbourne.—77o K.C., 390 metres SCL, Adelaide.—73o K.C., 411 metres 4QG. Brisbane.-800 K.C.. 311 metres. IYA. Auckland.—6so K.C., i 61.3 metres 2YA. Wellington.—s7o K.C. 526 metres. 3YA, Christchurch. - 720 K.C. 41M metres 4YA, Dunedin.—79o K.C, 379.5 metres 4YO. Dunedin.—ll4o K.C 2GI metres ANSWERS TO CORRESPONDENTS " 'Phones," Mataura.—To attach headphones to your set connect a .05 mfd. fixed condenser, a 10,000 or 15,0000 ohm potentiometer, and another .05 mfd. condenser in this order in series between the plate of the output pentode and earth. One of your headphone tags can be taken to earth and the other to the moving arm of the potentiometer. This will enable you to control volume in the headphones separately while the speaker is operating. 'Phones with a resistance of 1000 td 2000 ohms per earpiece would be quite satisfflctorv B. S.,'Mornlngton.—(l) The best method of attaching the leads to a terminal is to bare the ends and solder them together, and also to a length of fairly heavy gauge wire. This is then taken to the terminal. See that the soldered Junction is bound with insulation tape to prevent corrosion. The pipes should be at least three feet long and eighteen Inches to two feet apart. (2) Yes; the main point is to keep the earth around the buried article as moist as possible. . ~ " Listener," Ranfurly.—l am afraid your letter is altogether too vague for me to form much of an opinion. It may be that you are situated in a bad location and one not suited for distance; possibly there is some local interference electrically which is so much stronger than the signals themselves, or your set may not be correctly adjusted. In any case, with a set of that power and in that location, I think you are a little optimistic , in expecting to get anything like 100 stations. All I can suggest is that you get a serviceman to have a look over the set to see if everything is in order. If he can find no fault, investigate the matter of local Interference and your installation generally. I EMPIRE WAVELENGTHS Heception of the Empire station is at present best on the 20-metre band. Listeners who make a point of picking up Daventry on the various wavelengths may find this list of service to them. The Empire transmitters at Daventry can operate on any three of the following frequencies simultane-

ON SHORT WAVES Conditions have greatly improved on all, the short-wave zones during the last week. After about 6 p.m. it is now possible to pick up a large assortment of stations, and conditions get better as the night comes on. On any night when conditions are good one can hearthe Empire stations on more than one channel. There is also considerable activity on about 20 metres. The 30metre band is, in fact, getting positively overcrowded. The Australian shortwave stations come in as if Australia were located somewhere in Wellington Harbour. Lisbon, incidentally, may be heard on occasions in the evening. The call is CSW, and the wavelength just over 30 metres. Although it is usual to give short wavelengths to two places of decimals, the average tuning dial moves so little that one cannot tell the difference. Eventually short-wave services are contemplated in Greece, Sweden, Norway, and other European countries. All of them will be audible in New Zealand at some season of the year or another. AN IMPROVED "EARTH" Although the water-pipe ground is most commonly used by radio-users, it is recognised that, apart from the point of accessibility, this form of earth has nothing to recommend it. The water pipes carrying the house water supply pass through all sorts of conditions of earth. Most of their length is buried in ground which is often a very poor conductor. Again, the pipes often run for a considerable distance before entering the earth. Therefore the enthusiast who believes he has an excellent ground connection because his earth lead is only two feet from the water pipe would be sadly disillusioned if he knew the distance the pipe really went before it "earthed" his receiver. A poor earth is generally the cause of many defects, principal among these being lack of selectivity. The best way to obtain a good ground connection is to use an earth pipe driven into moist soil and connected directly to the set. Attention should be paid to the location of the earth pipe, and the lead to the receiver should be as short and as direct as possible. All that is required to make this earth pipe is 30 inches of one-inch conduit pipe, such as is used for electrical purposes, and one piece of sheet copper six inches by one inch. The conduit pipe is cut slantways with a hacksaw, the cut commencing two inches from one end. The enamel is now scraped off for about 18 inches, measuring from the end. A further piece is scraped for a depth of one inch. This is done from the top end of the tube. A series of quarterinch holes are drilled about one inch apart around the pipe. These extend from the pointed top up to the portion where the enamel remains. The sheet of copper should now be hammered into the form of the letter U, so that it will fit closely around the pipe. Two holes are drilled in this clamping strip, one to take a terminal and the other a three-sixteenth inch bolt, which is to be used to clamp the strip firmly to the pipe. The earth pipe is now finished, and may be driven into the ground. In dry weather the earth around the pipe may be kept moist by pouring the water down the pipe. HEADPHONE RESISTANCE Many users of radio receivers have the mistaken idea that the resistance of headphones is 'a measure of their quality. Actually headphones for radio reception of 2500 ohms resistance may be much better than others of 5000 ohms resistance. The resistance is determined by the length, size, and kind of wire used in their construction. Their performance is a matter of proper engineering design and the use of good materials. S SELIFISH LISTENERS The British Broadcasting Corporation recently arranged a programme designed to show how inconsiderate and indiscriminate use of a broadcast receiver can be annoying. The programme began with the playing of two gramophone records at the same time, and there followed other examples of the maner in which the " loud speaker nuisance" can disturb the peace of a neighbourhood. The corporation's public relations division commented oi, the effort in the following words:—" Tin listener whose idea of listening is to keep his set switched on at maximum volume throughout the broadcasting day; those who set their volume controls at maximum whenever dance music, or a talk, or ' music hall 'is being broadcast; and, worst of all, inconsiderate listeners who tune from station to station at 10-second intervals, heard vivid examples of the chaos that their selfishness creates. This ' straight talk' to the inconsiderate was not a broadcast to the Empire—but that was not because every overseas listener is guiltless of disturbing his neighbour's peace. There are, it is feared, quite a number who assume the right to choose a neighbour's listening for him, forget-

ting that excessive volume is unmannerly. Oscillation is a similar breach of the listener's good manners. Fortunately for British listeners, the majority of the medium-wave sets that they use do not oscillate, and so the listener at Home has left behind that evil at least. But some short-wave sets, in careless hands, can radiate piercing howls over a surprisingly wide area, completely ruining reception by any other set within range. In the famous words of the first chief engineer of the 8.8. C., 'Please don't do it'; consideration of the fellow on the other side of the garden fence is not only neighbourly decency, but helps one's own enjoyment." This statement is very much to the point, and might well be observed by all owners of receivers, as those .who live in relatively thickly populated districts will agree. One of the defences of those who persist in making their sets heard over wide areas is that if the reproduction is to be natural, it must be at a level comparable with that of the original. They claim that it is absurd, for instance, to make z military band sound like a penny whistle. In»this contention there is a lot of truth, but they omit entirely to consider the fact that to make as much noise as a military band would require considerably more power handling ability than there is in a dozen ordinary sets. To attempt to reproduce even a fraction of the equivalent sound energy only results in bad distortion.

ousiy:— Frequency Wavelength % Mc/s. Metres. GSA .. .. 6.05 49.59 GSB, .. .. 9.51 31.55 GSC .. ,. 9.58 31.32 GSD .. .. 11.75 25.33 ' GSE .. .. 11.86 25.29 GSF .. , .. 15.14 19.82 GSG .. , .. 17.79 16.86 GSH .. , .. 21.47 13.97 GSI , .. 15.26 19.66 GSJ .. .. 21.53 13.93 GSL .. 6.11 49.10 GSN .. .. 11.82 25.38 GSO .. .. 15.18 19.76 GSP .. .. 15.31 19.60