Coaxial wired broadcasting system with tone responsive program selectors

A wired broadcasting system comprising a wideband coaxial cable for carrying multi-channel programme signals from at least one programme source to a plurality of exchangers to each of which plurality of subscriber units for receiving a particular frequency band are connected, the said at least one programme source being constructed to supply the signals to the cable in different frequency channels, and each exchange comprising for each subscriber a switchable frequency translator for selectively translating any one of the said frequency bands to a predetermined other frequency band receivable by the subscriber unit, switching means controllable from the respective subscriber unit to selectively switch the frequency translator, and an output circuit constructed to supply the said predetermined other frequency signal to a feeder cable to which the subscriber is connected, a selector unit at each subscriber unit for generating control tones, wherein said switching means located at the exchange is responsive to said tones, a tone generator unit constructed to provide at least one master pilot tone to the said wide band coaxial cable, and a tone extractor unit at each exchange constructed to extract the said at least one master pilot tone from the said wideband coaxial cable for application to each subscriber unit connected to the exchange, the selector unit comprising tone generators responsive to the said at least one master pilot tone.