| 摘要 |
<p>An improved pay-TV-system, comprising a centrally located obfuscation signal generator, adapted to periodically pass to at least some TV-channels obfuscation signals, and control and communication device (12) to set which ones of the channels at the respective subscriber where unobfuscated receiving is authorized, comprising a centrally located coding device (K) to which a modulated TV-signal from the cable net (10) is passed, and which, within the band width of the TV-signal, via an obfuscation signal generator (13) passes to the modulated TV-signal data for the respective obfuscation signal, such as time, duration and frequency of the obfuscation signal, and, for each subscriber, a decoder (AK), comprising a sync unit and a filter, and adapted to receive obfuscation coded signals from the coding device, and, in dependence on control signals from the control and communication devices (12) on one hand, and the function of the sync unit on the other hand, to filtrate off the obfuscation signals on the channels where normal receiving is authorized in order to pass to an output terminal only decoded information signals. The system includes a logic circuit which is adapted to detect whether or not an obfuscation lies within the filter, and a device adapted to adjust the filter towards the obfuscation. Further, at least some of the decoding units (AK) are provided with a by-pass line, preferably including an amplifier (F), to provide a by-pass function.</p> |
