Abstract: An enhanced scrambled video signal, method for making an enhanced scrambled video signal and apparatus for enhanced scrambling of a video signal are all characterized by a pattern added to a video signal. The pattern is formed from a pair of segments, including a black segment and a white segment which forms a high contrast transition therebetween. The transitions vary in horizontal location from one horizontal line to the next. The pattern causes an unauthorized television receiver to mistakenly lock onto the transitions in the pattern, as if the transitions represented horizontal sync signals, thus scrambling the video display. The apparatus for inserting the pattern may be formed by a sync detector, a video amplifier, a multiplexor and a control logic device. The video amplifier sets the video signal to a DC reference level. The sync detector detects the horizontal sync of the video signal which is sent from the video amplifier.

Abstract: A scrambling system for a cable television system in which a group of channel frequencies are reused over a plurality of service areas includes an access controller, an encoder and a plurality of simplified scrambling units. Each service area receives different television signals on the group of channel frequencies. The access controller provides signal authorization information for a given channel frequency to a plurality of receiver/decoders located in the different services areas. The access controller also provides descrambling information corresponding to the signal authorization information to the encoder for the given channel frequency. The encoder produces a conditional access code by placing the descrambling information into a scrambled reference signal. An extracting unit removes the conditional access code from the scrambled reference signal and distributes the conditional access code to each of the simplified scrambling units operating at the given channel frequency.

Abstract: An interactive home information system having a node in television communication and data communication with a group of home interface controllers. At each home interface controller, there is a signal input for receiving television signals from the node over a cable television distribution network and a data transceiver for conducting data communications with the node. The node determines whether a home interface controller is requesting interactive service. For each interface controller requesting interactive service, the node assigns a television information signal to the requesting home interface controller. Thus, signal assignment is accomplished on a demand basis for those interface controllers determined to be placed in an interactive mode. Signal assignment may involve selection of a given carrier frequency. Alternatively, signal assignment may involve selection of a time slice.

Abstract: A system for scrambling a television signal by designating a horizontal line number on a pseudorandom basis and then stripping the vertical and horizontal synch components from the signal at each location of a frame except at the designated line.

Abstract: An apparatus is disclosed for transmitting digital data by radio frequency electromagnetic radiation, wherein the radio frequency transmitter of the digital data is electrically isolated from the source of the digital data. The radio frequency transmission is accomplished by symmetrical frequency modulation of a high frequency carrier, wherein the range of the symmetrical frequency modulation is responsive to the logical level of the digital data.