| 摘要 |
<p>1503051 Secret television WESTINGHOUSE ELECTRIC CORP 6 Aug 1976 [8 Aug 1975] 32820/76 Heading H4F Secret television transmission is effected by cyclically shifting with respect to time at least two segments of the video portion of each line of the video signal with the size of the segments selected randomly. Specifically each scan line is digitized and the resulting digital numbers sequentially stored in a random access digital memory from which they are read out beginning with an address which is randomly selected while the next line is stored in a second memory. The point within each stored data line at which read out begins is controlled by a random number generator, and to set the starting point of a matching random number generator in the receiver to thereby accurately restore the television line signals a binary sync code is transmitted during each even field vertical retrace period. To eliminate transient errors at the receiver twelve digital numbers are repeated at both the beginning and end of the shifted line during transmission. A cue pulse may be added just prior to the beginning of the active line of each shifted line which is used in the receiver instead of the pore sync pulse to phase lock the clock generator. For a colour television signal the clock generator is phase locked to the colour subcarrier.</p> |
