Interdiction method and apparatus with frequency change inhibit function

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 vary the sequence in which the voltage control words are read out of memory to modify the jamming pattern of the subscriber. In addition, according to one illustrated implementation, the loading of frequency control words to the latches in the sequence can be inhibited without changing the words in the memory. The sequential state machine will then in effect skip the deauthorized frequency control words and produce jamming signals at the previous frequencies. This provides flexibility in the system for either jamming or unjamming a specific channel to a subscriber for short periods of time. This allows a simple authorization and deauthorization technique without having to reload the frequency control memory or recalibrate a frequency control word for the specific channel selected.