THE WIRELESS WORLD

Otago Daily Times, Issue 23884, 11 August 1939, Page 2

THE WIRELESS WORLD

By Magna Vos

NEWS AND NOTES

Items ot 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.!! 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 -720 k.c. 416.4 metres 4YA Dunedin.—79o k.c. 379.5 metres 4YO Dunedin.—ll4o k.c. 261 metres ANSWERS TO CORRESPONDENTS F McW., Itanfurly.—lf the model you have has a pre-selector stage Incorporated it is possible that the set requires realigning, especially in that stage. A preselector stage sometimes develops an open circuit, which does not affect the sensitivity but seriously cuts down the selectivity. I would suggest that you have the agents check the set over, as they should know all these facts, " Transformer,” Timaru.—The two valves in push-pull are treated as though they were resistance in series, so that the total resistance is double. Each 2A3 has a load resistance called for of 2500 ohms, hence the total load resistance Is 5000 ohms. The square root of this value divided by the voice coil impedance—that is, the square root of 625, which is 25 to I—is the ratio required. This is for the case vvh*re the valves are running under self-bias arrangements. Should you require the valves to have fixed bias, the load resistance called for is now 3000 ohms each. Hence the total is 6000 ohms, and the ratio would now be 27.4 to 1. RESEARCH BUREAU’S FINDINGS As a result of the activities of its Listener Research Bureau, the 8.8. C. is able to say, for example, that in the British Isles nearly 24,000,000 listeners like variety, 13,500,000 appreciate talks, over 17,000,000 like plays, and nearly 10,000,000 light opera. It knows that nearly three out of four families have wireless sets, that more sets are switched on between 8 and 9 in the evening than at any other time, and that 8000 schools listen to school broadcasts. And the results are being increased, the scope of inquiry given wider application, every day. Not a word about the number who like “ serials.” A POWER FOR THE GOOD During his last trip to New Zealand Lord Nuffield formed a high opinion of the value of the Empire services, and wrote to the 8.8. C. to tell it about it. In his letter the motor magnate said: “Radio is a great power for good, Some people, say equally it has power to harm; but I don’t believe,that in the long run it can be so potential a power for harm, for the more virulent and vicious the propaganda the more likely if is to defeat its own ends. News with a constructive background based on the firm pillars of truth is bound to be beneficial to the world in the long run. By this I don’t mean that those responsible for our Empire broadcasts will satisfy listeners merely with news bulletins, however objective and accurate they may be. An Important point which crops up about the news is the cheerfulness and friendliness of the announcers. People that I have spoken to are all in favour of,, a cheerful framework, even when depressing news, has to be disseminated.” TELEVISION AND LIP-READING The exciting discovery that a new world is opening for the totally deaf was made by the lip-reading champion in 1930 during a visit to the television studio at the New York Worlds Fair. Obviously television will make radio entertainment possible for the deaf for the first time, but she. was more interested in the possibility that television may increase the opportunities of the deaf in the business world. Her first thought upon finding that she could read a speaker’s lips <?n a televised picture was that television would enable the deaf to do their own telephoning. Someone else 1 now has to act as an intermediary m telephone conversations. She saw a television demonstration for the first time with evident excitement. Later sne was interviewed in the television studio, and said that she was able to understand many of the interviewer s word s b telecast, such as “transmitting, “television receivers,” and ‘ Worlds Pair.” To make all of his words understandable to the deaf the participant in a television programme.would have to take special pains, keeping ms mouth in full view of the television camera and perhaps accentuating ms lip movements to some extent, she said. Probably no television audience has realised with such force the full impact of this new medium as the deaf. There was enthusiasm in her voice, despite the monotone which is customary in the totally deaf. BOOKED UP According to an official of the Australian Association .of National Advertisers (radio advertising agents), Sydney stations are- now almost completely booked up. and it is becoming increasingly difficult to “buy time on the air. One result is that the stations are able to insist on curtailment of advertisements, and it is predicted that before long only- sponsored programmes will be accepted. • This will mean that only brief announcements of the sponsor’s name and products will be heard at the beginning and end of his session, and that the day of the 500-word drivel will be ended. LIFE OF VALVES While it is difficult to assess the probable number of hours of service to be expected from the valves of a receiver, it is safe to say that under normal conditions they will function satisfactorily for at least several years. The actual period depends on the voltages applied to the valves, the types of valves, and the electrical and mechanical shocks to which they are subiected. Usually the first sign of approaching valve failure is a gradual falling off in sensitivity and volume It is a simple matter to remove the valves and have them tested in a tube checker. automatic volume control Everybody knows that A.V.C. means automatic volume control. Or does-it • In a modern , set what it stands for is automatic [sensitivity control tne sensitivity of the receiver being regulated by the strength of the signals picked up. When a powerful nearby station is tuned in, sensitivity is automatically and instantly reduced to bring the signal down to reasonable level; when a weak station is picked up the fact that the signal is weak means that it cannot cut sensitivity back, and thus it is audible This automatic change in sensitivity according to the strength of the station being received means that in general all signals tend to level themselves out to uniform strength—if strong they are cut down to normal, if weak they are boosted up to normal One disadvantage of A.V.C, (or A.SC.) is the noise between stations. The reason for this is simple enough. Imagine tuning to a station which is so weak as to be inaudible. The A.V.C allows the set to run flat out in an endeavour to find & signal; in other words, maximum sensitivity is used. In this ultra-sensitive condition the receiver picks up all the electrical interference that is going—from transformers in street circuits, from vacuum cleaners, frigidaires, and every kind of appliance, however small, as well as internal noises from valves, etc The bigger the set the noisier it becomes in such circumstances. This explains the crackling and rushing sounds that emanate from the speaker when between stations or when a transmitter goes off the air.