RADIO TOPICS.

New Zealand Herald, Volume LXIII, Issue 19235, 26 January 1926, Page 13

RADIO TOPICS.

BY THERMION.

THE DUUEDIN BROADCASTS. As an answer to the dissatisfaction of New Zealand listeners with the transmissions of the Dunedin broadcasting station, VLDN, there has appeared in a Christchurch newspaper a statement detailing the difficulties met with in the operation of that station. As Auckland listeners will be interested in the explanation, a condensed account of the statement is given below. The broadcasting station is said to be situated in a most unfavourable part of the exhibition grounds since in every direction in the immediate vicinity of the aerial are situated numerous electrical devices capable of interference with the transmissions. One amusement device is practically directly under the aerial, and is a serious source of disturbance owing to poor arrangement of its moving contacts. The effect of this on the transmitter is difficult to eliminate.

The transmissions of the programme have their own difficulties. In the first instance the station operatives have no control whatever over the programmes broadcast from the festival hall, the cabaret or the band rotunda. Hie events of the evening just " go on," and the station operators have to broadcast them as best they can. The acoustic properties of the cabaret are said to be far from ideal for broadcasting purposes. In the festival hall a great number of the artists totally ignore the microphones, and others will wander away from the microphone to the far corner of the stage to finish their items. The band selections also have troubles of their own. In some types of music the volume of the. band drops to a mere murmur, and is just audible to the crowd on the stand and consequently does not actuate the microphone. Again, when the weather is not suitable for outdoor programmes the band performs in one of the courts, and the music has to be broadcast just the same. This entails running temporary wires from the set to the court through a maze of electrical energy.

The above is, in brief, the account of the difficulties involved in the Dunedin broadcasting. The lack of co-operation between the concert organisers and the broadcasters is rather striking, and would be the most serious obstacle to satisfactory broadcasts assuming the modulation were satisfactory. A " BEAM" STATION. The first commercial Marconi " beam " station is to commence operation almost immediately. The station has been erected at Montreal, Canada, and operates on the principle of concentrating in one direction all the radio waves it generates, instead of, as in the caso of the ordinary transmitter, spreading the waves out in all directions round it. The beam system has been tried experimentally and the operations of the Canadian commercial stafion will be watched with interest by the wireless world. According to the contract with the British Government, the Canadian Marconi company has to guarantee a service of 100 words of five letters each a minute. It is stated that tests which have already been made have given a much higher rate. Such a speed is, of course, considerably above anything that an ordinary telegrapher can accomplish, so that auto> matic transmitters are necessary. The operator, by simply typing the message, transmits it in dots and dashes to a tape, and this tape, which runs through the transmitting machine, like a record through a player piano, makes the transmitter send out the corresponding signals. The speed of transmission is governed by the speed of the tape through the auto- ' matic transmitter. The corresponding symbols cut on the tape at the receiving end can either be read by operators, who transcribe them visually, or can be fed into a special typewriter, which prints the corresponding alphabetical characters. The Canadian station has been erected for telegraphic transmission, but could, if necessary, be used also for radio telephony.

RADIO SAFEGUARD OH TRAINS. A wireless device designed to check the speed of train engines automatically when approaching danger was tested recently in America over a 10-mile stretch of a certain railway. The inventor is Mr. Thomas E. Clark, of Detroit, who explains that the device depends for its operation on the propagation of electromagnetic waves in the track rails .with varying ■ wave lengths, which actuate a visual signal in the engine-cab. Should the,train be occupying a block, the rest of the rail surface within that block becomes automatically demagnetised, and another train entering -the block from the rear or front will ■ receive the danger signal and an automatic appliction of the brakes. The preliminary tests are reported to have been successful, and it is stated the Michigan Central Railroad has equipped ten locomotives with the Clark device. ANODE RESISTANCES. For audio-frequency amplifiction using resistance-capacity coupling there is frequently difficulty in obtaining noiseless resistances. The best type of resistance is wire-wound and can easily be made by the oxperimenter who has a little time at his disposal. It is first necessary to obtain a 3in. length of ebonite rod, two inches in diameter, the rod having eight slots 1-10-inch wide and about a quarter of an inch in depth cut in it. Wind 30 turns of No. 47 D.S.C. resistance wire in the first slot, and then a similar number in the second slot in the same direction. It is now necessary to return to the first slot and wind the same number of turns in the opposite direction, and then perform the same operation with the second slot. Then, again reversing the direction, return to the first slot and proceed as before, afterwards dealing with the next pair of slots in the same manner and so on. This process is undergone in order to make the resistances as non-inductive as possible. The actual amount of wire in each slot will depend on the value of resistance required, which should bo not less than 40,000 ohms. A value of about 80,000 ohms is usual. The resistance of No. 47 S.W.G. Eureka wire is 214 ohms a yard.

NOTES AND HINTS. The two Auckland broadcasting stations are "on the air." One of these was testing on Saturday night and apparently has no call-sign allotted to it. The other station, IYD, is transmitting on 330 metres oil Wednesday and Saturday evenings. Both stations are operated by local radio dealers. The housing for the transmitting plant of the new Auckland station, YLAK, has been erected. The roof is of corrugated iron, an almost certain source of eddv current losses. It will be interejiting to see whether the engineer installing the new plant will prefer other roofing material American radio manufacturers estimated that in 1925 they v.-ould sell 3.000.000 wireless sets and 20,000,000 valves, in addition to accessories and components to the value of £30,000,000. The receipts for the year throughout the industry are expected to exceed £100.000,000, constituting an advance of £40,000,000 on the figures for 1924. Kinks in the telephone cords, should be avoided as they will ultimately break the fine braided wire. Make a practice of untwisting the cords each time the 'phones are used and the cords will last much longer.