Abstract: A two channel audio scrambling circuit for a television signal encoding system includes synchronized digital carrier switching means for deriving two suppressed carrier, switched audio signals that are 90 degrees apart, and combining them into a single output signal. A digital phase shifter, supplied with a carrier related to the horizontal line frequency develops properly phased outputs for controlling electronic switches to produce two phase displaced digital carrier switching signals. A plurality of scrambling modes are determined by logic means under control of a vertical interval signal, a video inversion signal and a tone signal input for controlling the digital phase shifter to change the carrier frequency. Complementary decoding circuitry for recovering the so-encoded audio signals is also described.

Abstract: A multi-mode audio scrambling system includes an all-pass filter and a 90 degree phase shift circuit for supplying balanced modulators with 90 degree phase displaced audio information and 90 degree phase displaced carriers derived from the horizontal line frequency of a television receiver for producing a single sideband, suppressed carrier audio spectrum. A plurality of offset frequencies are derived from the horizontal line frequency and are used to further modulate the resultant signal to produce a single sideband displaced audio spectrum. A logic circuit selects the offset frequency (mode) in response to vertical interval signals, video inversion signals and audio tone or data signals. The final output is thus scrambled in different modes with different offset frequencies. A complementary unscrambling system is also described.

Abstract: A means for scrambling video signals by the application of a periodic scrambling waveform which has the effect of altering the normal amplitude relationship between horizontal sync and the video picture portion of a horizontal line uses the comparison between the brightness level of the video signal during a predetermined time period with a reference as a means for varying the amplitude of the periodic scrambling waveform.

Abstract: A fault tolerant, self-powered data gathering system is provided having a communication channel having at least three lines, a controller connected to the communication channel for receiving data messages from remote stations and for supplying power to the remote stations, the controller having a selector for selecting a pair of the three lines over which data messages can be received, the pair also supplying the power to the remote stations, and a plurality of remote stations connected to the communication channel, each remote station having a rectifier bridge connected to the three lines, the rectifier bridge accepting power of either polarity and bidirectional data flow, a power store connected to the rectifier bridge for storing power supplied by the controller, a data message apparatus for transmitting data messages to the controller, and a transmitter connected to the rectifier bridge and to the data message apparatus for transmitting the data messages over the communication channel to the controller.