Importance

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Abstract

A method and apparatus for scrambling a composite television signal and method and apparatus for unscrambling of the scrambled television signal are disclosed in the present application. The method of scrambling shifts at least some lines of video information relative to adjacent (preceding or subsequent) lines of video information according to a predetermined scheme, and deletes at least some portions of the signal which comprise synchronization or control information of a known or predetermined repetitive form from between at least some of the adjacent shifted lines of video information. The method of unscrambling applies a complementary shift to return the video information into proper time spacing and includes the insertion of any necessary synchronization information eliminated from the signal during scrambling. Timing information allows the unscrambler to reverse the scrambling operation and thereafter insert any necessary synchronization information. This scrambling technique maitaining at least essentially all of the video information thereby allowing faithful reproduction on a television. The system in addition to being secure, is compatible with communication channels used to distribute television signals and the apparatus for unscrambling the signal is relatively inexpensive and reliable.

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First Claim