Principles of audio-frequency wire broadcasting

Abstract

The quantitative limitations of wireless broadcasting have stimulated an interest in alternative methods of distributing programmes to listeners. Wire broadcasting has certain basic technical and economic advantages over wireless broadcasting. Wire-broadcasting technique has been extensively applied in Holland, where 50 per cent of the Dutch listeners have their programme service laid on to the house by a wire connection. Relatively slight developments of the same nature have taken place in Great Britain.ldquo;Audio-frequency rediffusion” is the most common form of “wire broadcasting” existing to-day. In “audio-frequency rediffusion,” programmes originally transmitted by “wireless” are picked up by a receiver located where reception conditions are favourable, and the output of this receiver is connected, usually by landline, to the input of an amplifier which raises the level of the receiver output to a value sufficient to energize at once a thousand or more loud-speakers connected to the amplifier by a conducting network.In common practice this network is supported on house chimneys, but sometimes it is carried on poles. The consumersapos; branch feeders are wired in lead-covered cable.The paper analyses the effects set up by the interaction of the reactances and resistances composing the network and the loud-speakers, and it shows that the received level, particularly towards the ends of the lines, varies enormously both with loading at certain audio frequencies and with audio frequency for a given loading.Certain generalized rules are laid down to indicate how the distortions incidental to this form of wire broadcasting may be partly minimized or wholly eradicated.The analysis of the network performance allows the preparation of a specification for the amplifier necessary to supply power to the network.