THE NEW 2YA

Evening Post, Volume CXXII, Issue 155, 29 December 1936, Page 8

THE NEW 2YA

OPERATION TODAY

ANTI-FADING AERIAL

AUTOMATIC CONTROLS

The new 2YA transmitter at Titahi Bay is expected to be in full operation in the regular service this evening, though officially it will be "testing" to bring it into complete order. The official .opening will be held towards the end: of .January. ;

The transmitter, putting 60 kilowatts into the aerial, ranks among the world's big broadcasting stations, and is of thoroughly modern design, and is notable for its very high aerial, supported by a mast a little over 710 feet high.

The waves radiated from a wireless aerial travel in all directions, not only all round, but up into the air as well. It is possible, by the use of elaborate arrangements of wires, to control the general direction to a high degree, as is done in the "beam" systems, but less easy to prevent a large proportion of the power being thrown off into the upper air. CAUSE OF FADING. The radio energy which travels into the upper air is reflected downwards by what is known as the Heaviside layer (about 80 miles up), and as it has thus travelled through a longer distance than that which has gone horizontally to a distant receiving station, interference between the two sets of waves occurs. The upper-air path is not constant, so that the interference varies, and fading results. If the direct and reflected waves reach the receiver with equal strength, this fading will result in the signals being actually silenced at intervals. It is evident that if the discharge of energy into the upper air can be stopped, there will be no fading. It is not possible to prevent all upward radiation, but it has been found that'a high aerial (the actual height is governed by the wave-length used; discharges a smaller proportion of energy upwards than a lower one. and thus,reduces fading. At the.- same time, by increasing the horizontal discharge, it extends the rea effectively covered. The Titahi Bay aerial is not as high as H should be to obtain tha maximum anti-fading effect. This would be obtained with a mast about 1000 feet high, but such a mast would cost about three times as much as the 700-foot mast, and the extra advantage Us not worth the money. THE BIG ANTENNA. The aerial, of the "semi-umbrella" type, is of the same type as is used at IYA and 3YA, and also at some Australian stations. It was designed by 8.8.C. engineers and is used at most of the British stations. There are three antenna wires equally spaced round the triangular mast. Supported at the masthead by insulators, they descend nearly vertically, the lower ends being held, by guys, about 150 feet from the foot of the mast, and then brought in nearly horizontally to the foot of the mast. Therethey are joined together and led to the tuning house, where they are coupled to the feeder lines from the transmitter. From the top of the big mast a "triatic" stay some hundreds of yards long is carried to another mast about 100 feet high, and" from this is suspended a: vertical aerial for 2YC, which is also to be located at Titahi. Prom'the base of the 2YC aerial to the base of the big mast there .run two lj-inch strips of copper, and from tliese, copper wires 700. feet long radiate outwards. The earth system comprises about twenty miles iof wire. POWER SUPPLY. The transmitters will be run with current from the Hutt Valley Power Board's circuits; but for standby purposes a generator is provided, of sufficient power to run a 5-kilowatt transmitter. In the event of a power failure, the main transmitter will be disconnected from the aerial and the 5-kilowatt plant connected. The 2YC transmitter will also be of 5 kilowatts. It has been stated that the new 2YA will be as big a medium wave station as any in the British Empire, but that is not so, because in Great Britain the power of two of the stations has been increased to 100 kilowatts, and there is also a long-wave station operating up to 150 kilowatts. As far as is known, however, 2YAis the only station in the Southern Hemisphere with a power of 60 kilowatts. In the Northern Hemisphere there are dozens with 60 kilowatts and over. POWER AND "COVER." The public may be disappointed with the strength of signal from the new station,'in view of the fact that its power is 60 kilowatts compared with the present 2YA's 5 kilowatts, but the strength of the signals is not in direct proportion to the power, but to the square root of the power, so that it will be only three to four times the strength of the present 2YA. With the improved aerial, however, the strength will be increased, so that it will be considerably stronger than the present 2YA over the whole of the Dominion. The matter of site comes into the matter also. The site at Titahi is a very much better one for the territory on the west coast of the North Island. Practically all the populated territory on that coast will be well covered. The sea is the best known medium for transmission, and mountainous country the worst, and there will be a distinct gain by having the station in that position. All the districts along the coast, such as Pal-, merston North and Feilding, with large populations will get a much better service from the point of view 'of steadiness and strength of signal than they have been getting. Other parts of the Dominion will not be detrimentally affected by the position of the station. Gisborne will get a much stronger field. The moving machinery has . bean kept to the very minimum consistent with high fidelity in transmission. The only rotating machines of any consequence are the filament generators. The filaments require a current of 800 amperes. The motor-generators are by-far the most economical method of supplying this current. The only other moving machines are the motors, the pumps for. circulating cooling water for the valves, and fans for the radiators. Distilled water is used to circulate round the valves to keep them cool, and passes from the valves into radiators, which are of very much the same construction, as motor-car radiators. Air is driven into the radiators by fans, and the heat is so dissipated. r AMPLIFICATION. The studio in the city will be used as formerly, and the speech and music v/ill be carried by wires, similar to telephone lines, from the studio to the transmitter at Titahi Bay. From these lines the music passes into a special amplifier where it is increased in strength before being fed into the transmitter proper. This amplifier is located in a studio specially designed /,->r the purpose. The walls, ceiling, and floor are lined with perforated zinc, providing an electric screen to keep out the field from the powerful transmitter. • Also housed In this screened room is the frequency control section of the transmitter. This unit Js ln;duplicate, and Is designed to keep

the frequency of the station (570 kilocycles) accurate to within 10 parts in 1,000,000. Both of these units, the special amplifier and the frequency control, feed into the earlier stages of the main transmitter in the transmitter hall, and they are both amplified by several stages until they reach the 5-kilowatt station and the special modulator. The output of this station can be fed either into the aerial system through the transmission line, or alternatively into a final amplifier, thence to the 60-kilowatt station, and thence to the transmission line of tho aerial system. In the 5-kilowatt station the system of modulation is the | Marconi-developed series modulation, developed some four years ago, and first used in the Auckland station. Its principal advantage is that it enables a high fidelity transmisison to be attained at comparatively small cost. Separate valves are fitted in the final stage, so. that in the event of the failure of. any one, another can be substituted, reducing the time of . replacement and the time the station would be off the air. The whole transmitter is designed along similar lines, so that separate equipment can bs brought into service with the minimum of delay. , SAFETY DEVICES. Another interesting feature of the transmitter is the automatic operation of starting and finishing. From the engineer's control desk the whole transmitter can be started up, and its condition watched as it is brought into operation step by step. This is maintained by a sequence of relays which are so interlinked that the transmitter cannot come into operation except in the right sequence. This means that when a relay is operated to bring one unit into operation it automatically closes a circuit in the next link in the chain, and unless that link is closed the succeeding unit cannot be brought into operation.

All the high-tension units are enclosed in metal screens, the doors into which have specially designed locks, and should any door,, be opened safety devices provide that the high tension is automatically disconnected from the unit contained in that enclosure. This would mean that for the moment the whole station closes down. The high tension supply for the 5-kilowatt unit is fed over mercury vapour valves. and the potential supply for this rectifier is 10,000 volts. A separate rectifier is used for the 60-kilowatt unit., also of mercury vapour valves, but the potential supply in this case is 18.000 volts. There is a regulator to keep the power supply corrected to such a degree that a rise of 10 per cent, can be provided for. Further voltage control is arranged for the high tension supply, which to a certain degree is automatic, and prevents the application of too high a tension until the valve is in a suitable condition to receive it.

As the first official daylight transmissions from the new station at Titahi Bay were begun only this morning, ther was little time for the reception of reports from other centres on the quality and volume of the transmission, and it v/ill be some days before a complete, summary can be made of the remarks which are expected from different parts of the Dominion, The night tests conducted . recently, however, evoked from those who heard them general praise which it is anticipated will.be echoed by the reports on the. regular transmissions.