Abstract: A content data distribution system uses a single key and multiple program authorization to transmit a plurality of programs in multiplexed data packets such as those used in Digital Video Broadcasting. A receiver has a memory, a descrambler and a processor. Authorization indicators are transmitted among said data packets and stored in the memory. The authorization indicators identify a plurality of authorized data packets corresponding to at least one authorized program and further identifies a plurality of unauthorized data packets corresponding to at least one unauthorized program. Only authorized data packets are output from a receiver in decrypted form. Null sets are substituted for unauthorized data packets. Data packet tables may be rebuilt as necessary to replace tables lost in null set substitution. One key is used to encrypt all programs. Alternatively, a number of keys fewer than the number of authorized programs may be used for encryption. The keys may themselves be encrypted for transmission.

Abstract: A content data distribution system uses a single key and multiple program authorization to transmit a plurality of programs in multiplexed data packets such as those used in Digital Video Broadcasting. A receiver has a memory, a descrambler and a processor. Authorization indicators are transmitted among said data packets and stored in the memory. The authorization indicators identify a plurality of authorized data packets corresponding to at least one authorized program and further identifies a plurality of unauthorized data packets corresponding to at least one unauthorized program. Only authorized data packets are output from a receiver in decrypted form. Null sets are substituted for unauthorized data packets. Data packet tables may be rebuilt as necessary to replace tables lost in null set substitution. One key is used to encrypt all programs. Alternatively, a number of keys fewer than the number of authorized programs may be used for encryption. The keys may themselves be encrypted for transmission.

Abstract: A tunable oscillating limiter threshold extension demodulator capable of demodulating video and other wide band width FM signals is described. A steering signal is generated to tune the oscillating limiter in response to the video output signals from an FM discriminator to which input signals from the oscillating limiter are applied. The steering signal is generated so as to be in proper phase relationship to track the frequency of the FM signal for modulating frequencies within certain critical regions and is reduced in amplitude over another region where proper phase relationship is not achievable because of unavoidable delays in the system. The steering signal generating circuit may be provided by a filter having a phase response characteristic such that the total phase lag of the system is small at the low frequency end of the band width and about 360.degree. at the high frequency end of the band width.