It is impossible in a book of this nature to give a detailed description of all broadcasting stations. All stations differ in many respects and if stations generally were described, certain remarks which would apply to one would not apply to others.
In order to give the radio enthusiast some idea of just what a big broadcasting station is really like, however, a description of one large station will be given. For this purpose 4QG Brisbane (The Queensland Radio Service) will be referred to.
Station 4QG, Brisbane, is situated on the roof of the State Insurance Buildings, George and Elizabeth Streets, Brisbane, and is a landmark for many miles around. At 4QG the whole of the buildings necessary for the carrying on of a broadcasting service are grouped under the one roof, there being no distant control of the transmitting apparatus as is the case in some of the other Australian broadcasting stations.
The whole of the buildings are of concrete and comprise administrative offices, reception hall, studios, instrument room, laboratories, and workshops.
The State Insurance Building is eight stories high, and an elevator service from its main street entrance carries the visitor to the main vestibule of 4QG. From this the offices of the Director, Chief Engineer, Inquiry and General Offices open up. An arched door leads to the main reception hall, which is built in the form of a double cross, and measures 56 feet by 56 feet at its widest points. This hall is tastefully decorated with moulded plaster, and is capped by a large moulded plaster dome supported by fluted pillars. The floor is of inlaid Queensland silky oak, and the whole hall has a very handsome appearance.
From the hall two studios, one a large one and the other smaller, open up. Each studio is built of double concrete walls. with an air space between. Floors and ceilings are packed with felt and sawdust, thus making the studios quite soundproof. Thus, a rehearsal may go on in one studio while actual transmission is effected from another. The larger of the two studios is naturally lighted with double sound proof windows.
From the reception hall, a corridor leads to the main instrument room in which the transmitter is housed. This is a large, airy concrete room with a high roof, well lighted, and (as is the case with the studios) artificially ventilated. Laboratories, workshops, and staff bathrooms open off the station. At two corners of the building two self supporting steel towers, each 100 feet in height have been erected to support the aerial system.
When transmission is in progress at 4QG, either of the two studios is used according to requirements. The use of two studios enables large delays to be avoided between items especially where, say a band follows a solo item of some sort. When such a programme is broadcast the solo is given in the smaller of the two studios, and during its progress the band is arranged in the larger. A quick change from one studio to the other prevents any great amount of delay.
The broadcasting of an item from the station necessitates a great deal of careful attention to detail on the part of the staff on duty. The microphone suitably placed in the studio reproduces the sound waves in terms of minute pulsating electrical currents, and these are carried via conductors to the main station building.
The transmitting equipment is of Australian design and manufacture, and is of very handsome appearance. It is built on the unit principle, but at the same time has the main controls handily situated on one panel so that the engineer in charge may make his main adjustments when starting up without having to walk across the room.
The equipment in the station consists of a speech amplifying panel, sub-modulator, modulator, rectifier, main oscillator unit, master oscillator, and the necessary inductances.
When the microphone currents from the studio reach the station they are delivered to the speech amplifying panel, which boosts them to the required strength, and then delivers them to the sub-modulator. This panel is really an amplifier, which further builds them up and passes them on to the grids of the main modulator valves.
It is not possible to rigidly follow the microphone currents right through until they are placed on the air, because, while they are being handled by the modulator panel other important functions are being carried out in the station by other pieces of apparatus.
The system of transmission comprises the master oscillator or "drive system," and is a system by means of which wireless waves are created by a master panel and then amplified at a radio frequency by a much larger panel known as the main oscillator. This system has the effect of enabling a constant wave length to be maintained. If it were not used, it would be very difficult to maintain the station on a definite wave length, because the swinging of a down lead from the aerial in heavy weather would cause a great variation of wave length.
Power is supplied to Station 4QG from the Electric Light Company's mains. This current is three phase and is at a potential of 415 Volts. It is stepped up from large transformers which may be seen at the bottom of the photograph of the rectifying unit. A system of tapped auto transformers enables the degree to which this current is stepped up to be controlled by the operator, and thus provides one means for the regulation of power output from the station.
The alternating current, after being stepped up, is rectified by a bank of six valves which may be seen in the top portion of the rectifier. It is then smoothed out by special condensers and by a smoothing choke. The rectifier unit at 4QG is capable of supplying continuously 24 Kilowatts of current. The current supplied by it is used for feeding the high tension to the plates of the valves in the master oscillator, main oscillator, and modulator panels the complete rectifying panel at times been jocularly referred to by the engineers of 4QG as the station's "B battery eliminator" and it is doubtful whether a more suitable term for it could he found.
The master oscillator alone has a normal power of 3 kilowatts, and is so designed that the power input can be considerably increased.
The photograph of this unit which is set out in this chapter shows the power condenser at the bottom and the various inductances on the top. This in conjunction with the tuning unit form the oscillatory circuit, and in this circuit the master oscillator produces continuous oscillations.
The main oscillator panel is the most imposing piece or apparatus in the whole station. On it is placed the main control switchboard, from which the voltages an all parts of the apparatus in the station may be handled.
It is interesting to note that the total power input when the whole plant at 4QG is in operation on maximum power is in the vicinity of 23 kilowatts. Of this about 7.5 to 8 kilowatts represents the power in the Aerial. This power has enabled large distances to be covered, and numerous reports of reception on a crystal at distances of more than 1000 miles from the station have come to hand.
Control of 4QG is effected both visually and audibly. The engineer on duty listens in at the station and hears the whole of the programme, and in addition to this has, from his seat at the control table, a clear view of quite a host of meters connected in various portions of the circuits.
These meters advise him just how each piece of apparatus functions. One of them in particular is his greatest guide, it is so connected that a needle will indicate the coming of any distortion just a second or two before that distortion arrives.
All the valves at 4QG develop great heat, and it is necessary therefore to cool them while the station is running. To enable this a special system of pipes is included in all panels, and a blower motor situated in a room adjoining the station blows a stream of air through these pipes on to the valves.