| 摘要 |
PURPOSE:To increase the tapping preventing effect, by coding the video signal with two types of sine wave signals. CONSTITUTION:A video signal (a) is coded by two types of sine wave signals (b) and (c) having different frequencies. The signal (b) is set at an n-fold frequency as much as the horizontal synchronizing frequency. In the same way, the signal (c) is set at an m-fold frequency. These signals (b) and (c) are added to the signal (a) to obtain a coded video signal (d). At the receiver side, the signals (b) and (c) plus their adverse phase sine waves are produced and added together. The coded video signal receives the modulation of amplitude by the added signal to decode the video signal. Accordingly various types of codings are possible by combining the sine waves with variation of their frequencies. As a result, the tapping preventing effect is increased. |
