| 摘要 |
PROBLEM TO BE SOLVED: To prevent illegal use by selectively inverting a fixed section of a synchronizing signal, attenuating and shifting the synchronizing signal and inserting a virtual synchronizing signal so as to make a horizontal synchronizing section irregular for ciphering to make viewing impossible. SOLUTION: Concerning a video signal, a synchronization separating part 8 separates horizontal/vertical synchronizing signals from the video signal to input to a logic circuit part 6. Then a video signal selective signal, a control signal and a deciphering information are generated. On the other hand, the video signal is inputted to a mutli-level shift and inverter part 4 through a sample/hold part 2. Concerning the video signal the fixed section of the synchronizing signal of which is electrically inverted and ciphered, a synchronizing signal is attenuated and shifted according to the control signal from the logic circuit 6 by a synchronizing signal attenuting and selecting part 18 through a third amplifier 5 and a ciphering mode is executed in addition. A virtual synchronizing signal is furthermore inserted by a multiplex virtual synchronizing part 13 to make the horizontal synchronizing section irregular for ciphering. Thereby viewing is impossible by a general TV receiver to prevent illegal use. |
