Interdiction method and apparatus with random mode jamming

Abstract

An off-premises method and apparatus for the interdiction of unauthorized channels of a broadband cable television signal includes common circuitry for adjusting the amplitude and equalization levels of the broadband CATV signals and one or more subscriber modules for generating jamming signals of different frequencies which are used to interdict one or more unauthorized channels. Each subscriber module is associated with a subscriber and is programmable and addressable to adjust the jamming parameters of that subscriber independently of other subscribers. Each subscriber module circuit comprises a plurality of latches, each of which is associated with one of a plurality of digital to analog converters. Each of the digital to analog converters drives one or more frequency agile oscillators with its analog output to generate the jamming signals. The subscriber module is based on a sequential state machine which loads frequency control words corresponding to the jammed channels from a frequency control memory into each latch on a cyclic basis. The state machine is adapted to modify the sequence in which the frequency control words are read out of memory to vary the jamming pattern of the subscriber. According to one illustrated implementation, the addresses of the memory are read out in a pseudo random sequence to produce varying jamming patterns but without changing a selected jamming factor for a selected group of channels. The pseudo-random pattern is generated by logically combining a predetermined address sequence with a random number seed from a seed generator. The random number seed can be varied either programmably or addressably to generate other pseudo-random jamming patterns. In another implementation the seed generator will evenly distribute the jamming energy of unused time slots to all the other active time slots.