| 摘要 |
Video signal scrambling and descrambling methods and apparatus for a subscription TV system (10) are provided which are compatible with other equipment (46) operating in accordance with pre-existing modes of signal scrambling and descrambling. Coded indicator signals (92, 96) generated in accordance with the invention are inserted into selected lines of video signals (90) before they are scrambled by a previously installed scrambler (18) located at a central office. The scrambled video signals, with indicator signals inserted, are then sent (55) to all subscriber locations within the TV system. At new subscriber locations (22), descrambling receivers, in accordance with the present invention, detect and decode the indicator signals and in accordance with a new mode of operation properly descramble the video signals. At old subscriber locations (46), previously installed descrambling receivers ignore the indicator signals and descramble the video signals in accordance with pre-existing modes of operation.
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