Sync displacement scrambling
First Claim
1. In a television signal transmission and receiving system of the type having transmitting means for developing and transmitting a television signal including nominally positioned horizontal and vertical synchronization signals and means for receiving said transmitted television signal and forming a synchronized video image in response to said nominally positioned synchronization signals, the improvement wherein said transmitting means includes means for replacing each of at least some of said nominally positioned horizontal synchronization signals with a surrogate horizontal synchronization pulse displaced in time therefrom and for inserting a video signal patch in said television signal at each position corresponding to a replaced nominally positioned horizontal synchronization signal, said video signal patch being derived from the portion of said television signal to which said surrogate horizontal synchronization pulse was displaced so as to cause said receiving means to reproduce said television signal in an unsynchronized and scrambled form.
3 Assignments
0 Petitions
Accused Products
Abstract
A subscription television system comprises means for broadcasting a scrambled television signal wherein the NTSC horizontal and vertical synchronization signals are displaced in time from their nominal positions. Each authorized system subscriber is provided with a decoder adapted for restoring the synchronization signals to their nominal positions to enable unscrambling of the broadcast programs for viewing. The synchronizing signals may be time displaced in a static manner or the time displacement may be dynamically varied as a function of time.
117 Citations
11 Claims
- 1. In a television signal transmission and receiving system of the type having transmitting means for developing and transmitting a television signal including nominally positioned horizontal and vertical synchronization signals and means for receiving said transmitted television signal and forming a synchronized video image in response to said nominally positioned synchronization signals, the improvement wherein said transmitting means includes means for replacing each of at least some of said nominally positioned horizontal synchronization signals with a surrogate horizontal synchronization pulse displaced in time therefrom and for inserting a video signal patch in said television signal at each position corresponding to a replaced nominally positioned horizontal synchronization signal, said video signal patch being derived from the portion of said television signal to which said surrogate horizontal synchronization pulse was displaced so as to cause said receiving means to reproduce said television signal in an unsynchronized and scrambled form.
- 10. In a television signal transmission and receiving system of the type having transmitting means for developing and transmitting a television signal including nominally positioned horizontal and vertical synchronization signals and means for receiving said transmitted television signal and forming a synchronized video image in response to said nominally positioned synchronization signals, the improvement wherein said transmitting means includes means for replacing the vertical interval associated with at least some of said nominally positioned vertical synchronization signals with a white level signal and a relatively wide surrogate vertical synchronization pulse displaced in time from the associated nominally positioned vertical synchronization signal.
Specification