IMPROVEMENTS IN AND RELATING TO WIRED BROADCASTING SYSTEMS

1499813 Wired broadcasting COMMUNICATIONS PATENTS Ltd 21 March 1975 [11 April 1974] 16226/74 Heading H4R In a signal adaptor for a wired broadcasting system a pilot carrier wave is derived from the broadcasting system and used to control the frequency of the output signals provided by the adaptor. As described the adaptor can be used to allow standard broadcast television or FM sound receivers to be used in the wired system. For television, broadcast programmes received over aerials 8 and 9 together with locally generated programmes from video cable 10 are transmitted at high frequency on respective pairs 4, 5, and 6 in cable 7, together with a crystal controlled locally generated pilot of about 20 MHz from oscillator 19. The signals may be received on special receivers 11, or on conventional VHF or UHF receivers 15 using an adaptor 16 which comprises a mixer 24, Fig. 2 (not shown) and a local oscillator (25) the frequency of which is determined by the received separated out pilot signal. The pilot and signal can be separated by a bifilar-T trap, Fig. 3 (not shown) and the oscillator may comprise a frequency multiplier, or a phase locked loop using a programmable counter in the loop. F or FM sound transmission a number of sound programmes can be transmitted on one line pair at 600 KHz spacing in the band 10 to 20 MHz with a 17À8 MHz pilot. The adaptor can include a frequency quintupler which with the mixer gives output signals in the range 99 to 109 MHz for reception on conventional broadcast receivers.