| 摘要 |
PURPOSE:To prevent simple interception by differentiating a compression rate of horizontal synchronizing part and vertical blanking period of a television signal. CONSTITUTION:A modulator 3 converts a video signal inputted to a video input IN and an audio signal inputted to an audio input IN into IF signals respectively. A television IF signal Fv and an audio IF signal Fa converted by the modulator 3 are returned to an encoder 2, where the horizontal synchronizing period and the vertical blanking period of the television IF signal Fv are compressed respectively by a different compression rate and a key signal including the information relating to both the compression rates synchronously with the leading of the horizontal synchronizing period of the television signal is superimposed on the audio IF signal Fa. The television IF signal Fv and the audio IF signal Fa are mixed by the modulator 3 and inputted to an UP converter 4, in which the result is converted into a signal with a prescribed frequency and sent to a transmission line such as a coaxial cable. |
