| 摘要 |
<p>A multichannel television access control system is disclosed wherein processing of the broadbande signal is performed by gated coherent RF injection on a plurality of channels, thereby effecting selective descrambling of an arbitrary subset of channels in a channel group. The system provides for a closed loop injection signal phasor control so as to maintain substantially constant relationship between the television signals and the injected signals. The combined signals are supplied to subscribers enabling the use of their cable ready equipment. The broadband signal is coupled to a broadband amplifier (104) via a power splitter (102). The injected signals are combined through line (114) with the amplified broadband signal by directional coupler (108), resulting in the composite signal on line (109). The broadband signal on line (109) is fed to the subscriber port (112) through directional tap (110). The injected signals forming together the composite signal injected at line (114) are generated by a digital broadband generator (136) feeding RF switch (116). During the time in which injection is required, RF switch (116) is at position (117) as shown in the figure.</p> |
