A video picture signal scrambling system for subscription braodcast or cablecast television systems which can scramble video signals without adversely effecting pictures received at a subscriber's terminal. The system includes a detector for detecting the brightness level of the picture signal over a predetermined interval, a comparator for comparing the brightness level with a first predetermined reference value and a scrambling circuit responsive to the comparator for inhibiting reversion of the picture signal when the brightness level exceeds the first reference value, and for selectively reversing the picture signal in response to changes in the brightness level in successive intervals of the picture signal.

A system for scrambling and descrambling a composite video signal having video program information, vertical sync pulses, and horizontal sync and blanking information includes an encoder and a decoder. The encoder scrambles the video signal by selectively biasing the horizontal information, selectively inverting the video program information and the non-biased horizontal information. The scrambled and nonscrambled portions of the video signal are modulated with data identifying the manner in which has been scrambled. The decoder detects the data identifying the manner of scrambling of the video program information. The decoder reinverts the sync by a fixed sequence which is triggered by normal sync. The decoder also selectively debiases the biased horizontal information, by a fixed sequence which is triggered by the normal sync, thereby producing the original composite video signal.

The present invention is directed to an inversion scrambler and unscrambler having pseudo-randomly controlled polarity-reversing switches to invert and re-invert, respectively, an audio signal so as to restrict the intelligent dissemination of the audio signal. To improve security of the scrambled signal, the audio signal is concealed prior to scrambling. Concealment includes clamping the original audio signal to a predetermined value and optionally offsetting this clamped signal prior to scrambling. The concealed signal is scrambled by inverting contiguous portions of the signal at pseudo-random intervals, accomplished by a polarity-reversing switching network controlled by a pseudo-random code generator. Upon unscrambling, artifacts will appear at the inversion points of the unscrambling signal, due to bandwidth limitations inherent in any transmission path. To mask the artifacts, track-and-hold circuitry is used to sample the unscrambled audio signal waveform level just prior to the artifact and hold this level throughout the short period when the artifact would occur.

A multichannel signal distribution control system, such as a CATV system, providing a plurality of video signal channels wherein selected channels are obscured by random noise jammer signals. The signal distribution system includes multiple output ports, each port connected to a respective user or subscriber. The random noise jammer signal is provided by a band-limited noise source and a signal translator which provides a noise signal band corresponding to the frequency of the channel to be selectively disabled. The resulting noise signal is added to the signals for specific individual subscriber output ports to obscure the signal on the selected channel of that individual subscriber. The multichannel signal distribution control system is controlled by signals provided remotely from a home office to each local jamming device by control signals superimposed on the multiple channel signal feed line.

A process for preparing organic carbonates, such as dimethyl carbonate, without the use of phosgene and with a high yield and selectivity to the desired carbonate, by reacting a formaldehyde-acetal with a source of oxygen, in the presence of a catalyst.