| 摘要 |
In order to selectively jam M selected channels to selected subscribers in a CATV system, each of M different oscillating signals, each of which oscillating signals has a duration longer than the duration of the horizontal synchronization signal of the television channel it is to jam and a frequency higher than the carrier wave of the channel it is to jam, are in turn added to the television signal circuits of those subscribers who are not authorized to receive the particular channel being jammed by the jamming signal being added. The television set of the non-authorized subscriber picks up the higher frequency jamming signal as the valid horizontal synchronization signal and therefore ignores the valid horizontal synchronization signal, with the result that the channel in question is unviewable on the television set of the non-authorized subscriber.
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