| 摘要 |
PURPOSE:To make decoding difficult externally and to change easily a disturbing wave pattern by transmitting superimposingly a digital pattern to a picture signal at the transmission side and eliminating the digital pattern superimposed while impressing the same digital pattern used at the transmission side in a way of opposite phase at the reception side. CONSTITUTION:A synthesizer 5 superimposes a modulation signal of a modulator 4 on a synthesized output of a synthesizer 2 and generates an output signal 3'. The output signal 3' is the synthesis of an input signal 1' and the digital pattern 2' and a modulation signal of the modulator 4 is synthesized. A digital pattern generator 8 uses this clock signal and generates the same digital pattern as that at the transmission side. An inverter 9 inverts the generated digital pattern and generates the digital pattern of opposite phase. A synthesizer 10 synthesizes the input signal eliminated with the modulation signal and the opposite phase digital pattern. Thus, the digital pattern superimposed on the input signal is eliminated. Thus, a picture signal of a base band is masked and the picture is ciphered. |
