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Abstract

The present invention provides a method and apparatus for scrambling and unscrambling television signals to prevent reception of acceptable signals by an unauthorized television receiver while maintaining the television signal recoverable by an authorized receiver. The present invention can also be used for reducing the necessary carrier signal power of a television transmitter. A transmitter (12) passes a television signal through at least one linear filter (30, 32 and 34) of the type that produces multiple time delayed signals of differing time delays. A receiver (14) receives the multiple time delayed signals from the transmitter and passes them through at least one linear filter (64, 66 and 68) to add the signals together so that one signal representative of the original is reinforced, allowing acceptable reception by an authorized viewer. In one arrangement, the linear filters are SAW devices. In another arrangement, the linear filters are of a type employing charge coupled devices and in yet another arrangement, the linear filters are of digital types. In yet another arrangement, high frequency linear filters are of a ferromagnetic type. Different scrambling codes are achieved.

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First Claim