Abstract: A scrambling and descrambling system and method for the video and/or audio portions of a broadcast TV signal, for example, broadcast by cable, microwave or communication satellite, includes a telephone modem at the descrambling receiver decoder box which is periodically, for example once per month for a few seconds, connected to a central computer of the head end operator. The decsrambling decoder box is enabled to receive the telephone call by a digital identification code broadcast periodically and associated with each decoder box. Each decoder box has a digital serial number in its Read-Only Memory (ROM) portion of its CPU (central processing unit) and an Electrically Alterable Read-Only Memory (EAROM) containing an alterable look-up table having for each program code a corresponding descrabling code to enable the descrambler.

Abstract: Selected interference frequency signals are inserted into the video or RF signal at the transmitter for scrambling purposes, either singly or in pairs. At the receiving end the signals are decoded by use of filters matched to the transmitted signal. The system allows different scrambling for each pay program thereby increasing the security relative to the prior art single frequency system.

Abstract: Each decoder has a random access memory storing program code numbers, a security number, a customer identification number, and program identification numbers utilized for billing purposes. Communication between each decoder and a central computer is subscriber-initiated. The program code numbers must be updated periodically by means of a computer-decoder transmission which takes place only after the program identification numbers have been transmitted from the decoder to the computer. During predetermined cycles in the system sequence, the read-out of the random access memory takes place in reverse order and starting at an arbitrary start point hard-wired into each decoder. Confusion signals are transmitted while program identification numbers already transmitted to the computer are erased in the decoder memory. The communication through the telephone network takes place by frequency shift keying.

Abstract: At the television transmitting end, the program audio signals to be encoded are limited to a range of 50 to 7,500 Hz. A 202 KHz signal is modulated by the so-limited audio signal and the resultant upper side-band is heterodyned against an upper side-band derived from modulating the 202 KHz signal by video horizontal drive signals. Only the lower side-band created by the heterodyning process is transmitted. At the receiver, the received single sideband signal is applied to a product detector whose other input receives the output of a horizontal drive oscillator operating in synchronism with the corresponding oscillator at the transmitter. The baseband audio signal is separated from the upper sideband signal at the product detector output by means of a low pass filter.

Abstract: The standard composite television signal is modulated onto an intermediate frequency carrier signal. The so-modulated signal is applied to the input of a first and second frequency converter for conversion respectively to a first or second UHF or VHF output frequency. The two converters are enabled alternately, each for a predetermined number of frames. The resultant signals are summed and transmitted to a receiver location. At the receiver location, the power is split along two channels. Two tuner-mixers, one in each channel, and tuned, respectively, to the first and second output frequency, respectively convert the incoming signal components having the first and second frequency to the same intermediate frequency. The two intermediate frequency signals are summed and converted to the proper frequency for reception on standard television receiver.

Abstract: A predetermined pattern of code signals is periodically inserted into the transmitted encoded television signal. The pattern is so chosen that a bistable circuit at the receiver changes state for each received signal. A counter counts the number of state changes and, if correct, a validation signal is furnished. The validation signal allows recording of the billing charge for the program and transmission of the decoded signal to the television receiver.

Abstract: The computer at the central office is connected to the automatic answering system either with or without ringing the subscriber's telephone. Tones sent by the computer to the subscriber system are filtered and compared to a reference signal and a connect signal is furnished when the comparator outputs indicate that the tones signifying the particular billing system have been received. The connect signal energizes a relay which connects the billing system to the telephone line. A holding circuit for the relay is also energized. A first time delay circuit furnishes a signal to start data transmission from the billing system to the computer a short time after receipt of the connect signal. A billing system furnishes an "access complete" signal deenergizing the holding circuit when billing data transmission is complete.

Abstract: Reference pulses of opposite polarity to the horizontal sync pulses are added to the composite television signal just preceeding each horizontal sync pulse. The video portion of the signal is inverted for randomly selected fields. Coding bursts are added to the composite signal to indicate whether subsequent field is inverted. Transmitter clamped to reference pulse level. Reference pulse used for AGC in decoder. Video portion of received signal inverted in accordance with coding bursts. Audio program signals encoded by modulation on suppressed carrier centered above audio range. Barker signals transmitted on normal audio frequencies.

Abstract: At the sending end randomly generated binary code number signals are inserted into predetermined lines of the vertical retrace interval. The code number signals are also processed in accordance with a program assignment code to change or leave unchanged a predetermined characteristic of the television signal. Periodically, program identification signals, each signifying a program identification number, are inserted into the television signal instead of the binary code number signals. At the receiving end, the program identification signals are utilized to address a random access memory which furnishes program assignment signals. The program assignment signals control logic circuits to process the code number signals in accordance with the same program assignment code utilized at the transmitter. The output of these logic circuits is then utilized to decode the received encoded signal.

Abstract: At the sending end, a plurality of high-frequency oscillators each furnish a signal having a frequency different from the frequency of the other of the oscillators. Timing signals derived from the television signal and signals from a random pulse generator are combined to furnish enabling signals for enabling the high-frequency oscillators during predetermined time intervals of the television signal and in a random order. A logic circuit which includes externally operable switches for setting up a program code assignment receives the enabling signals and furnishes an encoder control signal only in response to certain selected enabling signals. The encoder control signal changes the polarity of the picture signals relative to the synchronizing signals in the television signal. A mixer mixes the oscillator signals into the encoded television signal.

Abstract: A predetermined pattern of code signals is periodically inserted into the transmitted encoded television signal. The pattern is so chosen that a bistable circuit at the receiver changes state for each received signal. A counter counts the number of state changes and, if correct, a validation signal is furnished. The validation signal allows recording of the billing charge for the program and transmission of the decoded signal to the television receiver.

Abstract: Due to unavoidable timing and slope errors in the leading and trailing edges of invert pulses utilized in encoding and decoding of the television signal by inversion of the picture signal portion relative to the synchronizing signal portion, transients are generated. A clamping circuit clamps the television signal to a predetermined reference level for short time intervals around each desired switching time instant. The time intervals are sufficiently long to include the maximum possible variation in the actual timing of the switching time instants. A grey level is thus inserted at the encoder. At the decoder, a clamping circuit clamps the television signal to ground potential during the grey level intervals thereby balancing the DC components of the signal portions.