BEAM WIRELESS.

Press, Volume LXIII, Issue 18894, 8 January 1927, Page 16

BEAM WIRELESS.

AUSTRALIAN STATION. SATISFACTORY' TESTS. (niOll OUB OWJf COE3KSFONDEST.) SYDNEY, December 30. After years of planning and building the Australian beam wireless service is expected to commence operation between this country and England early in the New Year. The station in Australia is situated at Ballan, about 40 miles from Melbourne, and although the part for transmission to Canada is not yet complete, the section for traffic with England is daily in communication with the English reciprocal station. The tests so far have been of a preliminary nature, principally intended to permit of final adjustments to the transmitter being made, and to . enable the engineers at the British receiving station to adjust their apparatus to receive in the best possible manner the Australian signals. The tests have been highly successful. Special Aerials. One of the most striking features of the beam wireless station i 9 the aerial system employed. It is on the form of the aerial that the production of the concentrated radiation known as the beam depends. There are two different aerials at the Ballan station, one for communicating with Canada, and the other for working with Britain. Each of the aerials is supported on three lattice steel masts, each about 250 ft high, and arranged in a straight line, with about 1600 ft between the outer masts of each line. At the top of each of the masts is a steel crosspiece which serves to support a system of horizontal steel cables extending along the top of the masts. These cables are really the support for the aerial. A 9 a fact, many different aerials are employed in the beam transmitter. They are suspended in the form of single vertical wires from the cables along the mast tops, being suitably insulated from the steel structure of the masts and supporting cables, and the length of each aerial is carefully measured with respect to the wave length used. The line of masts for communication with England is so laid out that it is at right angles with an imaginary line joining Ballan with the English receiving station. The beam is projected in a direction at right angles to the line of the masts, and it therefore passes over the spot where the receiving station is erected. Coupling Box. Each cue of the vertical wires forming the aerial system is connected at ito base with a piece of apparatus known as n> coupling bos. The purpose of this box is to energise the aerial wire with energy supplied from the transmission room. Tlie method by which the beam is produced can best be understood by considering a simple analogy. Imagine a dozen tuning forks all vibrating at the same pitch, and arranged in a row above a basin of water. To the tip of each vibrating fork is attached a pin, with its point just touching the water surface. Each individual pin vibrating would tend to set up a series of ripples moving out in circles. If the distance between the vibrating pins is properly arranged in respect of the wave length of the ripples, each series of ripples will combine with its neighbours, and a clearly-defined concentrated wave, having a straight front instead of a circular front, from a singla disturbance will be produced, and_ it will advance in a direction at right angles to tho line in which the tuning forks are placed. At the beam wireless station the row of vertical aerial wires represents the row of pin-points touching the water surface, and the energy supplied by the transmission line through the coupling boxes represents the energy of vibration supplied to the pins by the tuning forks. As each pin tended to produce a series of waves spreading afl round the point where it touched the water, so does each individual aerial wire tend to produce a system of wireless waves advancing in all directions. As the waves from each of tho pins combined to form a concentrated wave with a straight front, so do the waves produced by the individual aerial waves combine into a concentrated wave in the wireless system. The buildings containing the apparatus for tha beam transmitter are comparatively small, and a large portion of them consists of a power-house for generating electric current to operate the transmitter. The valve, system is used to produce the current for exciting the aerials. The wave-length used is rather less than 26 metres, and this is absolutely unvarying. The transmitter produces currents which surge up and down the aerials more than 11,000,000 times a second and at an absolutely constant frequency. An important feature of the interior of the station is the relaying system, whereby telegraph signals sent at high speed from Melbourne over a trunk line are made to control the transmitter.