Abstract: The present invention relates to a technique for the synchronization of multiplexed television signals within each burst signals received at a remote station or satellite in a TDMA communication system from non-colocated ground stations. The technique employs a dynamic master/slave ground station arrangement where a first station signing on assumes the role of the master ground station. Other stations subsequently signing on synchronize their transmissions to the master station signal burst or the signal burst of the last station to sign on by using apparatus which monitors the received burst from the remote station, measures its own signal delay to the distant station and then phase-locks its local subcarrier clock to the master or last station's transmission burst. Dynamic transfer to the second station signing on occurs when the current master station terminates transmission for any reason.

Abstract: The present invention relates to a very fast acquisition phase-lock loop arrangement comprising means for generating an error signal between an input signal to the loop and an output signal of a voltage controlled oscillator (VCO). The generated error signal, over its possible range of phase differences, is transformed by a transforming means into an output signal comprising a predetermined nonlinear response. The output signal from the transforming means is integrated in an integrating means to generate a control signal for appropriately changing the output signal of the VCO. Noise performance can be significantly improved by cascading two or more of the present phase-lock loop arrangements.

Abstract: This present invention relates to a system for providing secure communications without bandwidth expansion using an encryption method called masking whereby a masking signal is generated at the transmitter using a secret key which includes a predetermined threshold signal-to-noise ratio level that when added to a frequency modulated (FM) signal produces an unintelligible signal. Any type of masking signal as, for example, a sine wave, an FM signal, or bandlimited Gaussian noise, may be used. At the receiver, the corresponding masking signal used by the transmitter is regenerated and subtracted from the FM signal before demodulation. Because of the FM threshold effect, perfect removal of the masking signal is not required. It is only necessary to subtract enough of the masking signal such that the resulting signal-to-noise ratio (SNR) is above the required threshold for reliable demodulation of the original signal.

Abstract: The present invention relates to a measurement system for characterizing device performance comprising a set of generating and measuring instruments which are connected to a controller via a data bus. The instruments provide the necessary bias and RF signals to the device and concurrently measure its performance. Primarily three functions are provided: (a) establishment of a desired input signal by the user or the controller and the monitoring in real time of the device performance, (b) taking of a set of measurements and interpreting the measurements to characterize the device performance, and (c) displaying the measured and interpreted data for immediate study and the recording thereof for subsequent use. The automated capability permits a user to tune a device and simultaneously optimize its parameters.

Abstract: The present invention relates to apparatus for placing digital words or a private key into a register in an integrated circuit in such a manner that it cannot be later read or modified from outside the integrated circuit for purposes of, for example, providing a secure communication system. More particularly, a special key register in the form of an externally programmable read-only-memory which is programmable from external to the integrated circuit is provided. The programmable register contains at least one extra bit which is not part of the private key for enabling the program line through a gating means and entering the private key into the appropriate locations in the register before a predetermined binary code is placed in the at least one extra bit location which disables the gating means and thereafter prevents the changing of the private key in the register.

Abstract: An echo suppressor (21, 22) monitors signal levels associated with the working environment of an echo canceler (16, 17) to prevent spurious transient responses from the canceler. These spurious responses typically occur before the echo canceler has had sufficient time to appropriately adapt which is also the time when a call is first established. At such times, signaling and maintenance testing are performed in a telecommunications network and the echo canceler tends to produce an output when there is no actual transmit input signal. The echo suppressor includes a comparator (26, 27) which detects the presence of this output and the absence of an actual transmit input signal and operates a switch. The switch prevents the transient echo from propagating on the transmit path.

Abstract: The present invention relates to a technique for transmitting both a video and a plurality of audio signals within a predetermined signal format which is compatible with a known signal format not normally used for television transmission. More particularly, the video signal is sampled at a first multiple of the video subcarrier frequency. The digitized video signal and associated video mode status bits are then multiplexed with the plurality of digitized audio signals into an N-bit frame format using a second multiple of the video subcarrier frequency which is less than the line frequency of the known signal format. The N-bit frames are then sectioned into Y-bit subframes and multiplexed with auxiliary and monitoring bit information comprising, for example, frame location bits for the Y-bit subframes using a third multiple of the video subcarrier frequency to generate a system signal format which is compatible with the known signal format.

Abstract: In order to control the transfer of packets of information among a plurality of stations, e.g., digital computers, the instant communications system, station and protocol contemplate first and second oppositely directed signal paths. At least two stations are coupled to both the first and the second signal paths. A station includes arrangements for reading (and writing) signals from (and on) each of the two paths. Signals are read from either path by an arrangement which electrically precedes the arrangement for writing signals on the path. If the station has a packet to transmit, it can overwrite a busy control field of a packet on either path. Also having read a packet signal from the path, a logical interpretation may be made within the station as to whether the path is busy or is not busy. If the path is not busy, the packet may be written on the path by overwriting any signal thereon. If the path is busy, the station may defer the writing until the path is detected as not busy e.g.

Abstract: The present invention relates to a technique for generating a Semi-Compatible High Definition Television (SC-HDTV) signal which can be sent over two present-day Cable Television (CATV) channels. In accordance with the present invention, a HDTV signal is formed comprising a line scan rate which is a multiple of the line scan rate of a current conventional TV signal. The SC-HDTV signal is formed therefrom by transmitting a first HDTV line as is and a second HDTV line as a field differential signal transmitted via QAM on the IF or RF carrier of the first line signal at a line scan rate of a current conventional TV signal. Arrangements are also disclosed frDconverting the SC-HDTV signal back into either a HDTV or conventional TV signal.

Abstract: The present invention relates to a multibeam antenna arrangement comprising a main focusing reflector, a doubly curved subreflector disposed confocally with the main reflector and a plurality of feeds disposed on a doubly curved focal surface of the antenna on which an image of the far field of view is formed. The subreflector is doubly curved in orthogonal directions to introduce a predetermined amount of barrel distortion for transforming a three-dimensional, non-rectangular, matrix in the far field of the antenna arrangement into a substantially rectangular matrix on the doubly curved focal surface of the antenna arrangement. Feeds are aimed such that a central ray from each feed reflected by the subreflector impinges a common point on the main reflector.

Abstract: The present invention relates to an antenna feed arrangement capable of providing a zero reflection response at a first frequency of interest and a maximally flat response at a widely separated second frequency of interest. The feed arrangement comprises a smooth-walled waveguide section at a first end, a corrugated waveguide section at a second end designed to provide the zero response at the first frequency, and a quarter-wave transformer waveguide section disposed between the smooth-walled and corrugated waveguide sections designed to provide the maximally flat response at the second frequency. The quarter-wave transformer section comprises a plurality of N corrugated waveguide subsections, where N.gtoreq.2, which comprise corrugation depths corresponding to the corrugation depths in the corrugated waveguide section.

Abstract: The present invention relates to an antenna sidelobe or interference cancellation arrangement including an antenna with a monopulse feed, for providing a sum and difference pattern signal, and an omnidirectional feed for providing a flat pattern signal. The flat pattern signal is used to appropriately shift the lobes of the received difference pattern signal in a first canceller section to substantially correspond to the location of the lobes of the received sum pattern signal. The shifted difference pattern signal is then used to cancel interference in the sum pattern signal in a second canceller section to generate an output signal at the cancellation arrangement which is relatively interference free over a wide band of frequencies.

Abstract: The present invention relates to a technique for recovering each of an entire analog speech signal and a modulated data signal simultaneously received over a transmission channel such as a common analog telephone speech channel. In the received composite signal, the entire modulated data signal is multiplexed within the normal analog speech signal frequency band where the speech is present and its signal power density characteristic is at a low level. Separation of the speech and data signals at the receiver is effected by recovering the modulation carrier frequency and demodulating the received signal to recover the data signal. The data signal is then (a) remodulated with the recovered carrier, (b) modified to cancel phase jitter and frequency offset errors detected during the data demodulating process and (c) convolved with an arbitrary channel impulse response in an adaptive filter whose output signal is subtracted from the received composite data and speech signal to generate the recovered speech signal.

Abstract: The present invention relates to a quasi-soft decision decoder for convolutional self-orthogonal codes which includes a multistage syndrome register, a bit detection means, parity check means and threshold logic gates. The bit detection means is augmented to render a "quality" bit in conjunction with each detected data bit which indicates the quality of the received signal level for that bit when compared with a predetermined threshold signal level. Memory storage is provided for storing the quality bits in parallel with memory storage for the data bits. Each of the threshold logic gates includes a separate group of active inputs from the syndrome register plus an associated one of the quality bits, each gate being arranged to generate an information correction bit which is dependent on a predetermined threshold level of corresponding input signals. The quality bit, therefore, provides an additional vote in the decision of whether a suspect data bit is erroneous or not.

Abstract: A method of etching a semiconductor crystal is given. The crystal includes elements selected from one of the groups: (a) indium and phosphorus; (b) gallium and arsenic; (c) aluminum and arsenic. The method comprises the steps of placing the crystal in an aqueous solution of H.sub.3 PO.sub.4 or HCl, and while the crystal is in contact with the solution illuminating predetermined regions of the crystal with light so that etching proceeds at the illuminated predetermined regions much more rapidly than at nonilluminated regions of the crystal. The method also includes focusing the light to a small spot on the crystal and moving the spot on the crystal so that a groove is etched in the crystal.

Abstract: The present invention relates to a single-mode single-polarization optical fiber which is capable of functioning as an in-line fiber polarizer which allows only one polarization of the fundamental mode to propagate along the fiber. In structure, the fiber comprises a central core region (10) and a cladding region (12) which is substantially in contact with the central core region. The various regions are formed such that the refractive index of an outer cladding region is greater than the refractive index of an inner cladding region but less than that of the core region. The arrangement of the present invention produces stress-birefringence between the cladding regions and the central core region sufficient to split the two orthogonal polarizations (n.sub..parallel. and n.sub..perp.) of the fundamental mode such that the desired polarization propagates freely and the undesired polarization is attenuated by tunneling through the cladding layers.

Abstract: The present invention relates to an antenna arrangement comprising a feed producing a predetermined feed aperture illumination and a plurality of sequentially arranged reflectors including a main reflector forming the aperture of the antenna arrangement. The present antenna arrangement also includes filtering means centered on a real focal point between two reflectors of the antenna arrangement. The filtering means is arranged to pass therethrough the central ray of a beam launched by the feed and for smoothing out discontinuities of the image of the feed aperture illumination in the area of the main reflector normally found without filtering. The main reflector is then made slightly oversize to intercept the smoothened-out image of the feed aperture illumination along a line which produces a predetermined level of edge intensity.

Abstract: The present invention relates to a portable transceiver and a remote terminal station each using at least two antennas with different polarization transmission capabilities for an adaptive retransmission technique. In the present adaptive retransmission technique, the terminal station transmits the same preamble signal in at least two time slots of a frame period of a time division sequence using the antenna receiving the strongest signal from the transceiver in the immediately prior frame period followed by a binary message signal using the same antenna. The transceiver receives each of the preamble transmissions from the terminal station via a separate one of differently oriented antennas and determines which antenna received the strongest signal. The message signal from the terminal station is then received via the antenna of the transceiver having received the strongest signal and also sends its response message signal on that antenna during a separate time slot of a frame period.

Abstract: The present invention relates to a space diversity combiner which includes two branches wherein separate multipath signals received from a remote source are propagated. The branch signals are combined and the combiner output signal is used for obtaining noncoherent spectrum measurements which are in turn used to account for both dispersion and noise in controlling the relative amplitudes and phases of the two branch signals to provide a maximum performance measure for the combiner.

Abstract: The present invention relates to a technique for transmitting an entire analog speech signal and a modulated data signal over a transmission channel such as a common analog telephone speech channel. The present technique multiplexes the entire modulated data signal within the normal analog speech signal frequency band where the speech is present and its signal power density characteristic is at a low level. Separation of the speech and data signals at the receiver is effected by recovering the modulation carrier frequency and demodulating the received signal to recover the data signal. The data signal is then remodulated with the recovered carrier and is convolved with an arbitrary channel impulse response in an adaptive filter whose output signal is subtracted from the received composite data and speech signal to generate the recovered speech signal.