Interdiction method and apparatus with pulsed 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. According to one illustrated implementation, the addresses of the frequency control memory are generated in subgroups of the possible time slots for a duration called a repeat cycle. Each additional subgroup is then sequentially addressed for the repeat cycle before the scheme is initiated again. This technique is termed 'pulsed mode' where subgroups of 8 out of 16, termed 'half mode', and 4 out of t16, termed 'quarter mode', are illustrated. This pulsed mode of operation results in channels which are jammed during the repeat cycle and then are in the clear for other times. This type of operation provides a great deal of flexibility in distributing jamming energy to a large number of channels which can be lightly jammed. The entertainment value of the channel is thus effectively destroyed without the need of oscuring the video 100% of the time.