RADIO AND ITS RECEIVERS

Sun (Auckland), Volume I, Issue 119, 10 August 1927, Page 14

RADIO AND ITS RECEIVERS

Conducted for THE SUN by C. M. Taylor, B.Sc., A.M.I.R.E.

LOCAL NEWS AND NOTES The executive of the Auckland Listeners’ League is meeting every week at present, the business in hand being a comprehensive critique on the broadcasting situation, the organisation of the referendum of listeners in the Auckland Province, the Radio Olympia and sundry other matters of import. A deputation from the executive was received by the general manager and the chief engineer of the Auckland Power Board on Saturday morning. The matter of pov/er line interference was stressed, and the manager stated his willingness to co-operate with the league in genuine cases, and it is suggested that listeners troubled with interference should make a precis of their troubles with any special remarks as to whether the interference was worse on wet nights, etc. This precis should be sent to the secretary of the league, P.O. box 512, Auckland, and the matter will be dealt with. Listeners should make reasonably sure that the interference is not from some other source such *s a motor used for domestic purposes, as in a refrigerator or a vibrating reed rectifier used for charging accumulators. Mr. Bartley, Mr. Glass and Mr. Edwards all questioned whether the interference most needing attention was not that due to howling valves, and these gentlemen, who are also keen radio enthusiasts, made a suggestion that is well worth consideration by lis-

teners—namely, that more good would be done by the addition of a stage of audio amplification than the suggested stage of neutralised radio frequency amplification. Their contention is that very often the radio stage is imperfectly neutralised, and is oscillating and radiating, and yet the operator is getting good signals and does not know he is interfering while, on the other hand, the regenerative detector operator cannot get undistorted reception if he oscillates, and the addition of an audio stage would do more to cut down interference than the suggested neutralised radio stage. The writer thinks there is quite a lot in this argument, and it would eliminate those growlers who sit on a station by the hour all unconscious of their sins. One can put up with the cheerful soul who suddenly “whoops” across and is gone again, but the other is impossible. A point which is concerning a number of amateurs is whether it is not time the Government amended its regulations with regard to the loose coupled aerial. The loose coupled aerial circuit is a much more violent radiator than the circuit, which has a damping load imposed on it by making direct connection from aerial to grid. This would enable British-built receivers to come into the country without alteration, a step which unfortunately for us, many of the British manufacturers seem unwilling to take. TELEVISION The news cables inform us that an attachment, costing about will be available for attachment to receivers, and we will be able to see as well as hear our entertainers. This mail brought a very nice publication from

the Bell Laboratories, describing the tests conducted with the television apparatus developed by the Bell Telephone Laboratories. The transmitter was a standard 5 k.w. Western Electric on 1,575 kilo cycles, and modulated 20 kilo cycles on each side of the carrier wave. A special receiver was necessary to deal with such a wide band. In the electrical transmission of pictures the transmitter is responsive to light waves. Its sensitive element is a photo electric cell, and the current from it varies in intensity according to the light to which it is exposed. When this cell is exposed to light emanating from successive small areas of a picture, there results a current with variations in intensity corresponding, and in similar order to the variations in light and shade of the picture. This is accomplished by using a film transparency of the picture, passing through it on to the photo electric cell a narrow beam of light, and moving the film uniformly and continuously so that the cell corresponds successively to the light from all the elemental areas of the picture. For the reception of pictures current variations are translated into variations of light intensity. This is done by varying the portion of light from a constant source, which is allowed to fall on a sensitised film. The film is moved across the beam, continuously and uniformly so that its successive areas are exposed in the same order and for the same time as the corresponding elemental areas of the original picture were exposed to the beam which actuates the photo-electric cell of the transmitter. The necessary synchronisation of the mechanisms foi driving the negative at the transmitter and the sensitised film at the receiver is accomplished by other waves transmitted from the radio station. In television a series of instantaneous views of a scene must be transmitted and reproduced at a rate of fifteen or more a second, so that an observer will detect no discontinuity of action. In broad principles the method is similar to that of the electrical transmission of pictures. A photo-electric cell acting as an “eye” rapidly scans the scene, viewing in orderly succession every detail and transmitting to the receiving station a varying current, the variations of which correspond to the differences in light and shade of the successive details. At the receiving station this current produces at each instant a.spot of light of a brightness corresponding to that of the detail of the scene the photo-elec-tric eye was observing at the moment it originated that particular amount of current. At each instant the position of this spot of light is also caused to correspond to that of the detail of the scene. The entire scene in successive details is thus reproduced for an observer. A NEW MICROPHONE This microphone, which is in use at 3AR, Melbourne, has proved so efficient that it has been sent to Sydney, where it impressed the engineers at 2BL and 2FC. It is a Western Electric broadcasting microphone of a new type. One of its chief features is the absence of the microphone hiss so well known in Auckland. The elimination of this background allows of very small sounds to be clearly picked up. Such sounds as the ticking of a watch and the sharpening of a pencil were recently broadcast from 3AR in a competition where listeners were asked to guess what the noise was. THE RADIO OLYMPIA Mr. A. R. Harris is considering the erecting of a sound-proof broadcasting studio at the Olympia, where all listeners might see what really takes place at the other end. This was done at the huge radio show in London, where one waited for three-quar-ters of an hour to get a thirty seconds’ glimpse, so popular was this exhibit. The writer hopes Mr. Harris will be able to make this exhibit, as it would be a splendid advertisement for radio in general and the company in particular.

A RUMOURED CHANGE FOR 2FC Persistent rumours are abroad in Sydney to the effect that 2FC intends to change its wave length to 550 metres. A high-power station has been testing on this wave length, but its call sign was not given as 2FC. No official confirmation of this rumour is yet available, but Sydney listeners are hoping for the best. This change would certainly be a boon to Wellington city listeners. HINTS AND TIPS Self-supporting low-loss coils, a hexagonal or octagonal bottle of any suitable width, is procured with the necessary wire. Pieces of stamp paper are placed on each of the flats of the bottle, and the wire is wound round the bottle over the paper and on top of the gum side. When sufficient turns are in place the paper is bent over and fastened securely down. The coil can then be slid off the bottle and is selfsupporting. CLEANING EBONITE When wiring a receiver a certain amount of flux generally adheres to the panel. Carbon tetra chloride is an excellent medium for removing grease and such substances as flux. The chemical can be applied with a brush or a pad of cotton wool. AIR-SPACED COILS The most difficult part of winding such coils is getting the spacing strips made. Corrugated celluloid cut into strips and used as formers make an excellent job, and the wire may be attached with a. varnish of celluloid dissolved in a liquid consisting of equal parts of acetone and amyl acetate. TO STOP TERMINALS ROTATING Before fitting to the panel make several radial cuts on the under surface of -

the terminal. This burr bites into the panel and effectively holds it when screwed up tight. SOCKETS FOR PORTABLE SETS The sockets in portable sets need to hold the valves firmly. The threaded sleeves in ordinary tumbler switches fit valve legs and have a small set screw which will hold the valve In tightly. RADIO POPULAR IN JAPAN; SETS TAXED In Japan radio is very popular, five Government-owned stations furnishing programmes regularly to a large audience. Nearly every house has an antenna, according to the visitor, but in Japan there is a tax of about 50 cents a month on all listening sets. Similarly, in the Philippines the Government imposes a tax on listening, amounting to 5 cents a month, in addition to collecting import duties on radio sets brought in. CORRESPONDENCE A.F., Parnell.—Such a battery would not be very suitable. *