Abstract: The multiplexer in a multichannel, secure digital communication system repetitively embeds a sequence of byte length uniquely coded synchronizing signals in each of n successive frames of one channel of a multichannel, time multiplexed digital bit stream. Redundant protective relay data and associated parity check data are embedded in four of the n frames in a second, preferably adjacent channel, with the remaining of the n frames in the second channel containing additional of the uniquely coded synchronizing signals. The time multiplexed serial bit stream is transmitted to a remote station, preferably by fiber optic communications media. The most recent bits of the received serial bit stream equal in number to the number of bits spanned by the two channels in n frames are retained in n-1 serially connected serial in, serial out shift registers. Sixteen bit portions, a frame apart, of the retained most recent bits of the serial bit stream are applied to n serial in, parallel out shift registers.

Abstract: A T-connection fiber-optical repeater employs redundant electrical-to-optical converters for generating optical signals to be distributed to terminal devices connected the repeater, and redundant optical-to-electrical converters for receiving optical signals from the terminal devices. Reliability is markedly increased by including one or two mixing stars in the fiber system between the converter and the repeaters. The number of converters and supporting circuitry that is needed can be reduced by coupling more than one fiber from the star or stars to each converter. The reliability of the repeater can be further enhanced by using redundant optical-to-electrical converters to receive optical signals from other repeaters and by using redundant electrical-to-optical converters to emit optical signals to other repeaters. Monitoring optical-to-electrical converters can be coupled to the stars in order to detect failure of electrical-to-optical converters connected to the stars.

Abstract: In order to avoid coupling losses, a fiber optic network employs wavelength sensitive devices to couple signals to a bus and split signals from the bus. A terminal device connected to the bus has an optical transmitter which produces signals at a wavelength that is different from the wavelengths employed in optical transmitters of other terminal devices connected to the bus. Furthermore the light is modulated to obtain a frequency channel identifying one or more terminal devices which are to receive messages from the bus. The bus is connected to a repeater which translates between wavelength and frequency channel. Frequency channels may be obtained by amplitude modulating or frequency modulating the light.

Abstract: A multi-star fiber optic network achieves improved access periods by grouping terminal devices into subnetworks that are connected to a bus, with token passing or collision detection being localized to individual subnetworks and with communication between subnetworks being conducted over the bus via non-interfering optical channels. The optical channels may be obtained by using light sources having different wavelengths or by modulating light at different channel frequencies. Each subnetwork includes an N-to-1 star which receives optical signals from terminal devices in the subnetwork and 1-to-N star which distributes optical signals to terminal devices in the subnetwork. Each subnetwork also includes a transmit repeater connected between the N-to-1 star and the bus to transmit messages which are addressed to other subnetworks on a unique channel, and a receive repeater connected between the bus and the 1-to-N star to receive messages on the channels assigned to other subnetworks.

Abstract: A multi-star fiber optic network includes a series of two or more passive transmission stars disposed in different local areas, each star serving terminal devices in its local area. A pair of repeaters between each successive star of the series receive optical signals on one channel and transmit the information on at least one different channel, thereby avoiding repeated reflections between successive stars. Wavelength multiplexing, frequency modulation, and amplitude modulation techniques may be employed to provide the different channels, one of which may be a baseband channel. Modified amplitude techniques may be employed to provide directional enable or inhibit signals on different channels.

Abstract: A T-connection fiber-optic repeater is used in a fiber-optic network wherein the repeaters are connected by optical fibers to other repeaters and the repeaters are also connected to stars, in such a manner that an optical signal can move from repeater to repeater without having to traverse a star. Each repeater includes optical receivers for receiving optical signals from the adjacent repeaters and from a nearby star and optical transmitters for emitting optical signals to the adjacent repeaters and the nearby star. Since signal reflections from the nearby star arrive almost immediately after signals from the adjacent repeaters, an inhibit circuit is used to gate signals from the nearby star when signals are being received from either of the adjacent repeaters. This avoids instability arising from repeated signal reflection without imposing a significant time delay as reflected signals propagate through long lengths of fiber.

Abstract: An audio scrambler digitally samples a continuous audio signal, scrambles the derived samples and inserts at least one scrambled sample in the unoccupied region of the video signals of a video system for transmission line per line as an analog composite audio-video signal. A RAM device is used for this purpose which has the digital samples stored sequentially, then read at random. A special memory arrangement is used as a scratchpad in order to insure that while addressing the RAM at random there will be no repetition, nor omission of a particular address. Provision is made for the insertion of more than one sample per video line, in particular while transmitting severe audio signals on the same video system. The same technique is used at the receiver end for unscrambling the samples once extracted from the video lines.

Abstract: The signal-to-noise ratio of a signal to be transmitted through a communication channel having an upper and lower limit in magnitude is sampled digitally and a common corrective factor for the deviations about the mean value of the signal is determined for amplifying the low portions of the signal without exceeding the limits. By a reverse process at the receiving end of the communication channel, the signal is returned to its original amplitude, thus reducing any noise superposed in the transmission.The invention is applicable to a video channel where the sampled signal is an audio signal. In such case, the deviations of the samples about the mean of the digital information of the audio signal are matched with the mean of the video channel between the black level and the maximum white level.

Abstract: An audio scrambler operates on segments of audio divided from a continuous audio signal to rotate head-to-tail the string of information contained in the segment by an amount which is at pseudo-random between the successive segments. When the segments are compressed to video format, the scrambled compressed audio signals are inserted into an unused line of the vertical blanking space of a television system for transmission with the video signals. The inserted audio is combined with decoy signals, also in the vertical blanking space to increase security of transmission. Concurrent scrambling of compressed audio signals and video signals is provided.

Abstract: A system for transmitting a secure television image is as disclosed. At the transmitter each line of the television image is digitized to generate a series of digital numbers representing the complete video line. The digital numbers representing the picture portion of each scan line are cyclically rotated by a random amount leaving the synchronizing portion unchanged. The digital numbers are converted to an analog signal which is filtered to generate a composite signal with the picture portion of each line cyclically shifted by a random amount. At the receiver the signal is digitized and the picture portion of each line is rotated to restore the picture portions of each line to their original position. The process of rotation is identical to that used at the transmitter except that the amount of rotation must be adjusted to restore all portions of the picture portion of the signal to their original position.

Abstract: In the recording of audio-video programs in which the audio is time-compressed and converted into television format, the video frames associated with a given audio frame are recorded in a group immediately following the audio frame, and picture-change cue signals are recorded at selected lines within the audio frame so that on playback, displayed video can be changed at preselected points in the audio frame playback. A number of video frames can be recorded between successive audio frames wihtout introducing any discontinuity in audio playback.

Abstract: In an audio-video program consisting of time compressed segments of audio information in the format of TV lines and video change signals associated with one or more of the audio segments, and video information to be displayed in response to the video change signals stored in separate portions of a magnetic or video storage medium, the playback of video information is synchronized to the playback of audio information by the occurrence of the video change signals present in the recorded audio information.