| 摘要 |
PURPOSE:To exactly prevent copying by adding mutually and intermittently a first pulse and a second pulse whose energy is actually one and the same as that of the first pulse which is delayed by a length of the back porch of a horizontal synchronizing signal comparing with the first pulse after a synchronizing signal in the vertical fly-back erasing period of a color video signal. CONSTITUTION:A pulse generating device 2 generates a first wide pulse C from a horizontal synchronizing signal B. A pulse generating device 5 generates a second wide pulse E from a synchronizing delay pulse D. A gate 11 generates a first wide pulse by using an output pulse from a switching signal generator 10, a gate 12 generates a second wide pulse, and a gate 13 generates a second synchronizing pulse; these three pulses are generated mutually and intermittently at every 0.05sec. The first and the second pulses are adjusted by amplifiers 14, 15 so that their energy are equal. A mixer 17 mixes a first wide pulse F and a second wide pulse G to generate a first adding signal K. An adder 18 adds a color video signal A with the signal K and a second synchronizing pulse I in order to drive a video head 20 via a modulator 19. |
