A method and apparatus, for jamming selected channels, in a CATV system, wherein six different pre-determined frequencies ("fx"), are generated at a head end, on a time divisional basis, which head end also generates a synchrinization signal ("sync. sig.") that identifies which fx is being generated, a multiple of receiver ends, each of which receives, at one input all of the TV channels' signals, the fx, the sync. sig., and a subscriber status signal ("SSS") that identifies the channels, if any, that the subscriber is entitled to receive, wherein the receiver end: (A) divides the received signals into: (I) TV channels' signals, SSS, and sync. sig., and (II) fx; (B) generates a local fixed frequency; (C) mixes the local fixed frequency with the fx, thereby creating a jamming signal; (D) decodes the sync. sig.; (E) decodes the SSS, to obtain the subscriber status information; (F) transmittes the TV channels' signals to the subscriber, if the subscriber status information, indicates that subscriber, is entitled to receive at least some or all of the TV channels; and (G) combines the jamming signal, with the TV signals, going to the subscriber, when the created jamming signal, is for a channel, that subscriber is not entitled to receive.

A video scrambling and descrambling arrangement utilizes plural scrambling characteristics including a predetermined scrambling waveform and a selectable one of a plurality of phase relationships with respect to the video signal to be scrambled. Descrambling is achieved by combining with the scrambled video signal a correspondingly phase shifted, inverted version of the scrambling signal. Scrambling and descrambling can be implemented in analogue or digital forms. The information required to achieve descrambling is contained in the scrambled video signal, preferably in an unscrambled portion thereof.

A frequency generating means, generates an initial frequency of greater amplitude than the amplitude of a television signal carrier wave. The generated frequency is compared to a reference frequency which would be suitable for jamming one of the channels to be jammed. If the generated frequency is too high or too low, the frequency generating means generates a new frequency which is, respectively, either lower or higher than the initial frequency it generated. If the new generated frequency is still higher or lower than the reference frequency, the frequency generating means generates another new frequency, which is respectively, either lower or higher than the previously generated frequency, but by a lesser amount than the amount by which the previously generated frequency differed from the frequency generated before it. The generation of new frequencies continues until one of them is within a desired range of the reference frequency, at which time the generated frequency is stored in memory. The same procedure is used to obtain memorized frequencies to be generated by the frequency generating means for jamming each channel to be controlled. On a time divisional basis the frequency generating means generates the jamming frequencies which are transmitted to each of the subscribers who are not entitled to receive the channel they are jamming. Periodically the jamming of channels is briefly stopped and the jamming frequencies are re-calculated and re-memorized, then the calculation process stops and the jamming resumes.

A pulse generator for generating pulses for modulation onto a carrier or subcarrier of a composite television signal is provided. The pulse generator includes a memory such as an EPROM for storing one or more waveshapes. Each stored waveshape is defined by a sequence of addressable values representing the amplitude of the waveshape as a function of time. A selecting circuit such as a microprocessor selects one of the waveshapes in the memory. A counting circuit responsive to a clock signal controls the address lines of the memory to read the amplitude values corresponding to the selected waveshape from the memory. The amplitude values are supplied to a digital to analog converter to convert the amplitude values to an analog pulse. The pulse may then be filtered to remove clock noise. The resultant signal is supplied to an amplitude modulator for modulating the signal onto a carrier or subcarrier of a composite television signal.

Apparatus for broadband signal distribution is equipped with a detector for detecting when the apparatus is open and is further adapted to receive an entry code generator. If the entry code generator is not installed or, if installed, fails to generate an entry code which matches an authorized entry code stored in the apparatus, the apparatus enters a particular mode of operation whereby service provided by the apparatus is interfered with. The entry code generator comprises a circuit board for coupling with an electrical connector of the apparatus having at least one ear which precludes closure of a cover to the apparatus. A method of screening access to the apparatus from others than authorized service personnel includes waiting a predetermined period of time for coupling the access code generator before service is interfered with. Furthermore, the stored access code may be changed or the predetermined time varied by addressable command from a headend of a broadband signal distribution system.