| 摘要 |
PURPOSE:To secure the reliability of data communication even when the performances of system's equipments degrade by superposing a key signal and a data signal on a sound signal at a timing corresponding to the horizontal blanking cycle of a video signal. CONSTITUTION:In a data decoder 2, the key signal and the data signal are superposed on the sound signal corresponding to the horizontal blanking cycle of the video signal by amplitude modulation. In this case, even if a distortion caused by a video source influences the sound signal, since both the key, signal and the data signal are subjected to the same compression-distortion during the said cycle, they are corrected by an AGC amplifier 8. Consequently, a stable detection output is obtained. Therefore, even when the linearity of the CATV system degrades, the reliability of data is not lost.
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