| 摘要 |
1522033 Wired broadcasting COMMUNICATIONS PATENTS Ltd 27 Oct 1976 [29 Oct 1975] 44500/75 Heading H4R In a wired television broadcasting system in which a number of programme signals are available on separate conductive paths to each of a plurality of programme selectors controllable by respective subscribers to the system, the selectors being either remote controlled or on the subscribers premises, the conductive paths are divided into groups, each group having a number of pairs of channels, with the channels of each pair having carrier frequencies which are offset by an integral multiple of half the line scan frequency and the phases of the carriers of the channels in the different pairs differing by an odd integral multiple of 90‹. As described carrier sources 11 and 12 provide carriers of about 8À9 MHz which differ by half the line scan frequency, each carrier source feeds a phase splitting transformer 13, or 16, Fig. 2 (not shown) to provide two outputs, 180 degrees out of phase, which feed respective phase shifters 14, 15, 17, 18, Fig. 3 (not shown) which each produce two outputs which are relatively shifted in phase by Œ45 degrees relative their input. The outputs of the phase shifters 14-18 feed respective modulators 27 to be modulated by respective programmes 28, and fed to the distribution network 29. |
