British empire broadcasting

Directional transmission to Australia, India, South Africa, West Africa and Canada, the 5 zones of the British Empire, is used, the best wave-length being chosen according to distance and path conditions. As Africa subtends too wide an angle to permit of useful concentration of radiation, it is divided, and this division also enables different wave-lengths to be used at the same time, which is necessary as West Africa and South Africa are at different distances. Each of the 5 zones has its own aerial array, each array containing at least two aerials tuned for different wave-lengths. For programmes on alternative wave-lengths there are two transmitters, with facilities for complete interchangeability between them and all the aerial arrays. For wave-length changing, the transmitters are shut down and the h.f. inductances changed, due to the wide range of wave-length covered (16.9 to 50 m.). The paper continues with a full description of the Empire broadcasting station of which the distinctive features are: economy in layout; supply taken from a ring main, no prime movers being installed; acoustic treatment and electrical screening of speech input rooms; crystal control, to 40 per million, on each of eight wave-lengths; frequency characteristic within 2 db from 50 to 8000 cycles; carrier power-output 12 kW; modulation up to 95%; thorough safe-guarding of all equipment.