3LO ON SHORT WAVE

Radio Record, Volume I, Issue 9, 16 September 1927, Page 13

3LO ON SHORT WAVE

MELBOURNE STATION’S KQUIPMENT. The well knewn broadcast station, $1.0, Melbourne, has now cominenced transmitting concerts on a short wavyelength, ‘This is a big enterprise and calls for a lot of technical skill and special equipment. The programmes are being given in the city studio in the ordinary way, ‘and passed on fo Braybrook (eight ‘miles from: Melbourne) by land linc. The wave-length is 29.8 metres, and ‘the power drawn from the mains will be 15,000 watts. At Braybrook the output’ from the studio is applicd through a cline amplifier and sub-modulator unit to the grids of the modulator proper, ‘which in turn is coupled to the plate of the special short-wave oscillating valves. These valves are of tmnique design, and are enclosed in metal screens in order to distribute the high frequency losses over the whole of the glass envelope and thus reduce the risk of puncture at the high potentials used. The oscillator is worked on the amplifying drive system through the stages of magnification-modulation taking place on the last stage. The ‘output from this is then fed through

a specially designed coupling cireuit through a "lecher’ feed to the distant ‘aerial. ‘The lecher lines consist of two highly insulated, tightly stretched wires supported on miniature telegraph poles. The energy from the transmitter is fed into the base of the aerial system by means of a special coupling. Steps are taken to prevent radiation from the lecher system and to eliminate refiection so as to ensure the maximum transfer of energy from the oscillating apparatus to the aerial, The advantages of this system are that the aerial may be kept. free from interference likely to be caused by conflicting electric fields in and around the actual generating apparatus, buildings, and other factors likely to cause absorption ‘due to the enormous intensity of the electro-magnetic ficlds set up at fre-

quencies of the magnitude of those to be used for these tests. | Electrical Screening. | The various units of the transmitting equipment are electrically screened from each other, and the frames and panels made of brass. The. circuits are so balanced that all fields induced in the frames are neutralised. All high frequency portions of the equipment are supported on plate glass strips to eliminate dielectric losses. The potential on the plates. of the main transmitting valves will be 8000 volts, supplied by a specially constructed_ three-phase double wave rectifier and associated smoothing unit. With this equipment 31,0 Melbourne will have the most modern and most powerful short-wave broadcasting station in the southern hemisphere, which should he capable of being heard in any part of the. world. All the apparatus was designed and built in Australia by Amalgamated Wireless (Australasia), Ltd.