RADIO RECORD

Greymouth Evening Star, 28 July 1932, Page 4

RADIO RECORD

NOTES FOR LISTENERS-IN

(By

“Reception” )

A RADICAL CHANGE. NEW TELEVISION SYSTEM A new idea concerning television, departing entirely from conventional principles, has been suggested by R. Thun. “Why complicate matters at the receiver in the way you do? argued this original thinker. “Your ray must, I agree,' move along line after line so as- to cover the whole picture surface; and in doing so it must .also reproduce the variations in light and shade representing the original subject. But .you go to endless trouble to control it so that it travels with a uniform speed, in exact synchronism with the uniform speed at the transmitter; and, having done this, .you have to produce your light and shade by making your signals control —in addition —its intensity. Surely this is rather like cutting a large hole 'in the door for ttie big dog, and a small hole for the puppy? For if you make your ray travel quickly where you want shade, and slowly where you want light, you will kill three birds with one stone. First, you will save time over the dark parts, where detail is not so essential, and have that extra, time to spare for the bright pajts, where you want all the detail you can get. ■ Secondly, you will get your light and shade without the complication .of haying to modulate the intensity of your ray, since the more slowly it ■ moves over a certain spot the brighter will ft make that spot; and, finally, since the ray can now be kept always at its highest intensity, .you will raise the whole level of brightness of the image.” ' , RADIOS in, MINES' Miners, in-some of the South Yorkshire coalfields now hew coal to the strain of dance orchestras. Radios have been installed in a number of the pits and' men find the' stress of ' toil relieved, by the- latest jazz tunes ■ from first-class London orchestras or , by operatic selections from some well-

known band. < Wireless installations have' been * tested of late in many mines with the ? idea of ’saving life. Hitherto miners r cut off in the works by explosions or

T falls of roclt have had to rely on th.e ■ underground telephone, which was usually “wrecked when the accident oc- * burred. Now, by means of portable < l-adio sets,’entombed men may be able td keep in constant touch with rescue parties and thus greatly facilitate . e.scape. ' Meantime the radio has been acclaimed in coal pits for entertainment purposes and managers report that it . helps rather than decreases output. TELEVISION TRIUMPH : A .crowd of 4000 sat enthralled in the darkness of a London -movie theatre on June 1, watching the Derby by television. Across a little white screen Oft by 7ft. they saw the. flickering black and white images of horses racing toward the winning post. >- They could see the crouching figures of the jockeys and even distinguished some of the stripes ./they wore. • v When at the finish- the bunch of

horses flashed past the television cam- ‘. era and the announcer’s voice relayed the result, there were shouts of “Marvellous! Marvellous!” from all parts of the house. Then the. lights went up and Mr. J. L., Baird, television inventor, walked shyly on the stage, < greeted by a storm of cheering. ; It was the first demonstration of .. television on such a scale. When it was over, Mr. Baird was too excited to say a word, but later.he said it had been a “reasonably .successful experiment,. considering the great technical ■.difficulties involved.” Three large drums, each with 30 mirrors fixed around the circumference, were rotated synchronously both at Epsom Downs and London, so that • pictures thrice the normal size were, obtained. The images to be transmitj ted were reflected by mirrors to photoelectric cells, and the resulting electrical signals were flashed over three - land lines from the television caravan | on Epsom Downs to the movie theatre. | Inside the hall signals were made to control light valves placed in front of three arc lamps. The lights from these were projected on to appropriate receiving-mirror drums and thence to the screen.

ELECTRIC SHOCKS y The. following facts written by an expert are illuminating. He says in “Popular Wireless” how a shock actually kills does not seem to be too definite. There are those who say that electricity kills by sheer destruction or burning of the tissues. In many respects the effect, too, is akin to drowning; and just as in drowning artificial respiration may “bring a victim back to life,” so it should be used to restore a person who has been electrocuted.

Medical opinion holds that in cases of electrocution artificial respiration should be continued for at least four hours after* a person collapses. People have actually recovered more than four hours after apparent death. Electrocution by J.ighlning is, of course, another thing. Colossal force;) are involved and the effect is. more violent. There is usually a hole burned in the top of the head where the current enters and another at. the heel The nerves and bio id vessels may he completely burnt up, and there is extensive scorching.

What voltage is necessary to kill a man? This question is always being asked, and the answer—-strictly speaking—is that volts do not kill; it is the current, i.e, the amps. Actual experiments have shown that J of an ampere passing through some vital pari of the body will result in, death. Half an ampere certainly kills. Since ; the human body has a fairly high resistance, which varies according to the moistness of the skin -md so on it takes over 1000 volts to pass half an ampere through-a- man. Given 1500 volts you should be able to kill the dfiest-skinned person, while in some cases 600 volts may do the trick.

NEW HOME OF 8.8. C. 22 SPECIAL STUDIOS All the studios and broadcasting rooms in the new home of the British Broadcasting Corporation are contained within a vast central tower, with a wall of solid brick, averaging four feet in thickness, writes Nelle M. Scanlan. A corridor runs round this central tower, and opens into all the adjoining offices, which are grouped, like a shell completely round the inner tower. This gives the offices a maximum of light and air. There are approximately 700 people now engaged at Broadcasting House. It seems a great many, but when the complexity and vastness of its work is considered, and the precision with which it carries out its job, it is readily seen how the number can mount up. As the various programmes require a different type of studio, not only in size and construction, but in its acoustic properties, twenty-two studios are provided. Down in the basement is a small theatre for vaudeville and light musical programmes, with stage, spotlight, and accommodation for a small guest audience, which helps in this type of entertainment. There is also a studio for chamber music on the same floor. Every studio has double doors,. rubber-edged and perfectly fitting. The main concert hall, which will accommodate a large symphony orchestra, and an audience of 700 people, rises through three floors of the tower, with a sloping auditorium and a gallery. A tiny miniature chapel, two stories high, with gallery, and a high silver window, with columns, is used fpr all religious services broadcast. It has an atmosphere suitable for such programpies. Every item, is carefully rehearsed, and up in the mechanical control room, where men. sit at a row of lights and buttons, with headphones on, I watched one man recording in a log book all the mechanical points, good or bad, in the rehearsal. Some they can counteract. When a studio is engaged, a red light for 7A or 3B as the studio may be numbered appears throughout the whole concern, a warning that nothing must be done Jo interrupt in any way. When a. band or orchestra is playing, a musician with the score in front of him, .sits in the adjoining listening-room, a small anti-room attached to every studio. There is a glass panel between all these rooms, usually a glass circle, so that without disturbing, observation is possible. The music controller can adjust the volume of sound, and in some cases they can even soften the brasses and bring up the fiddles.

HUM DIFFICULTIES There is no standardisation among manufacturers as to the physical arrangement of windings on power transformers, and two designs of equivalent Output and of equal technical merit may behave quite differently in the matter of inducing “hum” voltages in an L.F. transformer. This form ,of interaction is often responsible for a noisy background. The moral of this is that, when constructing a mains-op’erated receiver from a published design, the possibility of encountering “hum” troubles as a result of substituting a transformer of different make from that specified should be borne in mind. Before finally mounting the power and L.F. transformers, a test should be made, in order that their relative positions may be changed experimentally, if the need for doing so should arise. . CONDENSER RATINGS

The following remarks by A. L. M. Sowerby, M.Sc., an acknowledged expert on condensers, are worth careful consideration by all those interested in this übiquitous little component. Writing in the “Wireless World” he says: We hear frequent reference to the voltage rating of condensers, meaning in every case the voltage at which the condenser may safely be allowed to work. It is necessary to draw attention to the fact that there are many condensers on the market which carry no more information than a “test voltage” which they have withstood momentarily before leaving the maker’s hands.

The magnitude of this test voltage js a matter which concerns the manufacturer only, and there appears to be no reason/why-it should be communicated to the public, who are not interested in the tests the manufacturer chooses to apply to his products. In some factories the test voltage is double that at which the condenser is expected to work in actual service, while in other-cases it is not advisable I ,to run a condenser at more than one-third of the test voltage. It is possible that the discrepancy arises through varying duration of test; a condenser to work on 200 volts might be adequately tested cither by a momentary application of 600 volts or by having to stand up to 400 volts for a longer period. It is, in any case, quite certain that a condenser grandiloquently marked “500 volts” is only reliable, in the absence of any more detailed information, for voltages up to about 180 at most. The more modern makers either mark their condensers with working voltages, or at the least give this information in their catalogue, by stating the working voltage corresponding to each test voltage. In any case, it is the' user’s responsibility to choose a condenser which its maker guarantees as safe for operation at the voltage which he proposes to apply.

THRESHOLD HOWL Almost all who have constructed wireless receivers have been troubled by “threshold howl,” which takes place as the detector is passing into the oscillating condition under the use of reaction. It is sometimes extremely stubborn in resisting cure, unless the cause is recognised. According to an English journal, the effect is always due to the presence of radio-frequency currents in the low-frequency amplifier. and in a short-wave receiver this can be brought about by interaction between the output and aerial circuits After seeing that this form of reaction is not responsible, the remedy lies in fi'termg high-frequency current iron.