THE WIRELESS WORLD

Otago Daily Times, Issue 23690, 23 December 1938, Page 2

THE WIRELESS WORLD

NEWS AND NOTES By Magna 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 in the following Friday. IYA, Auckland.—6so k.c., 461.2 metres 2YA. Wellington—s7o k.c.. 526 metres 2BL, Sydney.—74o k.c., 405 metres. 2FC. Sydney.—6lo k.c., 476 metres. 3AR, Melbourne.—77o k.c., 390 metres SCL, Adelaide.—73o k.c., 411 metres 4QG, Brisbane.—Boo k.c., 311 metres. 3YA, Christchurch.—72o k.c.. 416.4 metres. 4YA, Dunedin.—79o k.c., 379.5 metres. 4YO. Dunedin.—ll4o k.c.. 261 metres. ANSWERS TO CORRESPONDENTS “ Filament,” Enfield.—(l) No. unless your battery is being charged very often and allowed to gas for some time on each occasion, The liquid should never be allowed to drop below the top of the plates in the battery, and these should be covered by at least a quarter to half an inch. (2) The only advantage is that you get a smoother flow of power, but you are put to far more expense and trouble. “Four,” Mosgiel.—Your volume control Is evidently faulty, and you should have it seen to as soon as possible. Was the noise noticeable when you demonstrated it to the agent? TWO MILES OF AERIALS At the new radio-telephone station which the British Post Office is constructing for communication for the United States the aerial arrays will extend for two miles, and will consist of 16 separate units erected in a line between the receiver and the United States. Each unit will be a single wire supported about 50ft above the ground, arranged in diamond shape, about 200 yards long and 60 yards wide. Each of the units is connected separately to the receiver building through an underground “ cable ” consisting of a copper rod at the centre of a 2-inch tube. This is the arrangement which was referred to in the cables about eight weeks ago, and which will, it is hoped, eliminate fading and distortion. NOISY LOUDSPEAKERS Reports from various parts of Europe show that some countries are still concerned about noisy loudspeaker reproduction. Stockholm forbids the use of the loudspeakers between 11 p.m. and 7 a.m., and Copenhagen will not allow excessive volume after 10 p.m. An Interesting case is reported from Belgium. There is apparently no regulation for dealing with reproduction which becomes a nuisance, but one set owner who persisted in loud reproduction was held to be giving a public performance, and therefore liable to copyright royalties to the composers whose works were being “broadcast.” FOR MORSE PRACTICE When practising Morse signals with a buzzer the sound is very different from the musical buzz of real wireless, but with the following simple combination of instruments almost the identical sound may be obtained. The Instruments required are a buzzer, sending key, a small telephone receiver, battery of two dry cells, and a dish of water. The main circuit is formed of the key, the battery, and the buzzer. In parallel with the buzzer are the telephone receiver and the dish of water, Into which the two wires dip to form the circuit. The ends of wire should be dipped in shellac varnish, or the sound in the receiver will be louder than that of the average wireless message. The interrupter of the buzzer should be tightened, making the “note" more highly pitched. When not in use the key should be left “ open,” or the battery will soon become useless. CHEAP GERMAN MACHINES Two or three years ago the German Government instructed radio manufacturers to construct three-valve sets to be retailed at about the equivalent of £3 15s in English money. It is claimed that nearly three millions of these receivers were turned out at no profit to the factory. Now orders have been given for the production of an even cheaper machine, a two-valver, at a much lower cost. The use of metals coming from abroad must be avoided, and the chassis is made of pressboard. The amount of copper and iron has been cut down to about 25 per cent. Purchasers are to be given the option of paying cash or having the instalments spread over 18 months. Needy persons are to be given assistance to enable them to acquire a machine, and a rebate of half the license fee (two marks) will be granted in approved cases.

DAVID LOW BROADCASTS David Low, the New Zealand cartoonist, famous for his brilliant work in London, broadcast to New Zealand last week. It was his first Empire broadcast since 1934, when he spoke on his experiences in art. Low was heard as a contributor to the series of talks “As 1 See It.’’ It was a weekly newspaper in Christchurch that first Eublished— and paid half-a-crown for-r----ow’s work. To-day he is 47. He was born in Dunedin, and was 11 years old when the Christchurch weekly bought his cartoon. But that early triumph did not convince his parents that they had an artist in the family, and young David was trained for the Church! PUSH-BUTTON TUNING

Equipment for tuning from station by merely touching a button has almost become standard in all parts of the world. In one or other of its forms it has been included in more than 50 types of receiver available, the receivers varying in price from about £ls to more than £6O, and taking in their range car sets, mantel and console models and elaborate gramophone combinations.

Fundamentally push-button or “automatic” tuning depends for its continued success upon the care in the design, choice of materials, and methods of assembling and testing numbers of seemingly insignificant parts hidden below the chassis. Constancy of electrical values of these parts in all conditions is absolutely essential, because, except in a few cases, the receiver is unable to correct even minor discrepancies. Much ingenuity has been shown in designing the mechanical arrangements for bringing the right components into Circuit or for setting the tuning units to the proper values. There are two general methods in use. In one the usual tuning arrangements are provided with means whereby they may be rotated to a desired setting without supervision by the operator. In the other scheme a number of sets of components, one set for each station that is to be tuned instantaneously, are provided, and switches are fitted whereby only the desired collection of components is put into circuit when required. In arrangements in which the conventional type of tuning units are driven to predetermined positions, the drive may be performed by motors controlled by the push buttons or by dials which are rotated in the manner of telephone dials or by rods which can act through racks and other arrangements to turn the whole condenser shaft to the proper positions while the rod is being depressed. In all systems different sets of stations may be chosen for “ automatic ’’ tuning, but in some the choice is relatively limited. For example, it is possible that No. 1 button can only be set to pick up stations within a certain band, No. 2 within a neighbouring band, and so on. This is not a great hardship, because the allocation of frequencies throughout New Zealand is such that each band will usually include a local station, and few systems are fully effective with weak stations. There is little to choose between the two general systems on the score of reliability and accuracy. They both depend upon the quality of the components of the receiver. Motor-driven systems have been criticised because of the time lag that occurs between touching a button and a station becoming audible. The pre-set circuit system operated by choosing the suitable circuit is instantaneous. On the other hand, the motor system is more flex-

ible in that all the stations that may be chosen for “ automatic ” action may be very close together in the whole band, and it lends itself to a “cruising” action in which a band is searched and •the mechanism stopped as soon as a suitable point is reached. A system which has a truly automatic adjustment. that is, a system of valves and circuits operated by the receiver itself to take care of mechanical errors and “ drift,’ is best, but the extra equipment makes it expensive.