Abstract: Systems and methods for a distortion monitoring system that detects an abnormal amount of signal distortion occurring in a transmission system. The distortion monitoring system includes a system amplifier section for amplifying and coupling an input signal to provide first and second outputs and a distortion monitoring section for processing the second output. The amount of distortion present is represented by an output from the distortion monitoring section of the system. In one embodiment, the distortion monitoring section can include an envelope detector for receiving the second output signal, a lowpass filter coupled to the envelope detector for cutting off frequencies below the Nyquist rate, and a voltage amplifier coupled to the lowpass filter for amplifying the signal.

Abstract: A cable television system provides conditional access to services. The cable television system includes a headend from which service “instances”, or programs, are broadcast and a plurality of set top units for receiving the instances and selectively decrypting the instances for display to system subscribers. The service instances are encrypted using public and/or private keys provided by service providers or central authorization agents. Keys used by the set tops for selective decryption may also be public or private in nature, and such keys may be reassigned at different times to provide a cable television system in which piracy concerns are minimized.