Abstract: A microwave stripline package provides symmetrical ground currents while permitting discrete components such as diodes, terminations, capacitors, etc.to be used. The package comprises a pair of face-to-face printed circuit boards, each of which is formed of a dielectric having a ground plane on one surface. The discrete components together with a printed circuit are assembled on one of the boards while a portion of the dielectric of the other board is cut away to provide mechanical clearance for the circuit components. Matching portions of the dielectrics on either side of the printed circuit are cut away to receive a pair of metal blocks which contact both the upper and lower ground planes in order to form a screened enclosure. The dimensions of the printed circuit within the screened enclosure are selected to provide impedance matching with the stripline outside the enclosure.

Abstract: A thin wall, stainless steel transformer case of rectangular box configuration is comprised of edge welded steel plates with its sidewalls and end walls bearing vertical, U-shaped bonded channel members of copper for mechanical reinforcement of the case and for forming transformer heat dissipating fins. Stainless steel reinforcing channel members are similarly bonded to the outside of the case bottom wall and the cover. An epoxy fiberglass strap spanning interiorly between the sidewalls of the case at its upper end and bolted to opposed brackets press the transformer core against the bottom wall of the transformer case. A pair of deformable tubes sealably project through the cover for effecting vacuum evacuation of the interior with the cover sealed to the case and for feeding insulating dielectric liquid to the transformer case interior. The tubes are pinched off and sealed after filling.

Abstract: An automatic recycle circuit is disclosed for use in a process or apparatus of the type wherein process or equipment conditions are monitored to detect an abnormal condition. The automatic recycle circuit accepts inputs from monitor circuits which are intended to cause recycle operation and monitor circuits which are intended to cause complete shutdown and reacts appropriately to each type of input. With respect to those inputs from monitor circuits which are intended to cause recycle action, the automatic recycle circuit is capable of permanently shutting down the process or apparatus if the detected abnormal condition has a duration exceeding a first predetermined time or abnormal conditions are detected a predetermined number of times within a second predetermined time period.

Abstract: Phase and amplitude modulation of single or multiple pulses and/or dual polarizations are used in a digital communications system which transmits multidimensional codes. Four dimensional code transmission is specifically disclosed, although the scheme may be extended to eight-dimensional and even 16-dimensional code transmission. The four-dimensional codes are constructed by mapping a digital word into two two-dimensional plane as two sets of x and y coordinates. Signals proportional to these x and y coordinates are used to modulate a transmitted pulse or pulses. When a single pulse is used to transmit the four-dimensional code, polarization modulation is used. A signal proportional to the square root of the sum of the squares of the coordinates assigned to both the horizontal and vertical polarizations is used to control the total RF amplitude of the pulse.

Abstract: A solar cell is constructed such that the losses resulting from radiation damage are reduced without sacrificing efficiency in the unirradiated cell. This is done by using a first conductivity type junction on the front of a high resistivity cell and a second, opposite conductivity type junction on the back of the cell. The two junctions are separated by an intrinsic region, and the cell potential, which is normally reduced by using high resistivity substrate material, is instead raised by using the second junction. The cell includes a reflective back surface and a non-reflective front surface to further enhance light absorption within the active cell volume. The reflective back surface is formed by polishing the substrate. The non-reflective front surface is a multi-pyramidal or V-grooved surface formed by preferential etching of the substrate material. The front electrode is a fine geometry grid deposited over the front surface of the cell.

Abstract: A redundant microwave configuration providing a highly flexible routing of a plurality of inputs to a plurality of outputs is characterized by at least two switching layers wherein each switching layer comprises a plurality of four port switches and the switches in at least one of the switching layers are connected in a ring, corresponding switches in the layers being interconnected. This redundancy configuration is not limited to microwave applications only but could be implemented at all other frequencies. One microwave configuration employs 2N amplifiers between said switching layers as building blocks to provide N inputs to N antenna ports. This configuration allows any combination of (m-N) amplifier failures without loss of service, where N .ltoreq. m .ltoreq. 2N. In other configurations, only one type of switch is used and fewer than 2N amplifiers are used for N inputs and N outputs.

Abstract: Bit rate compression in a digital communications system is provided by transmitting voice information from n telephone circuits over the capacity conventionally allocated for transmission of voice information from n/2 circuits without appreciable degradation in quality. Alternatively, a doubling of the number of voice circuits may be provided with transmission at the same bit rate required for conventional transmission of voice information. Each frame period, at the transmitter, all n circuits are serviced and, utilizing an adaptive predictive encoding scheme, a maximum of only 3/8 n unpredictable samples in the given frame are transmitted over the available channel capacity.A sample assignment word (SAW), which identifies the circuits corresponding to the unpredictable samples, is transmitted therewith.

Abstract: A logarithmic echo canceller is disclosed which simplifies the hardware of the canceller by (a) using a logarithmic format for both the sampled voice signal x.sub.i and the coefficient h.sub.i, (b) using sophisticated algorithms for performing the different computational tasks, and (c) using analog techniques for echo subtraction and error signal generation. The incoming signal is sampled in a sample and hold circuit. The sign of the sampled input signal is sensed and its absolute value is converted directly in a special analog-to-digital converter into an A-law companding code. The whole digitized sample x.sub.i is multiplexed and stored in a plurality of shift registers. An average or pseudo rms value of the samples is computed, and the samples are compared in a comparator with the stored average or pseudo rms value, and if the sample is greater than the average or pseudo rms value, a signal enables updating of the existing value of h.sub.i stored in the H-register.

Abstract: A plural cavity waveguide filter comprising a plurality of cascaded waveguide cavities each resonating in first and second independent orthogonal modes is disclosed. The cavities may be either square and/or circular resonating in the TE.sub.101 or TE.sub.111 modes, respectively. The filter makes it possible to realize the general class of coupled cavity bandpass transfer filter functions by providing that the input and output couplings to the filter be physically connected to the first physical cavity. A general set of canonical couplings can then be achieved within the structure.

Abstract: A cover slide for a solar cell comprises a plurality of converging lenses arranged to focus the incident light so that it does not fall on the grid lines of the front electrode of the solar cell.

Abstract: A digital voice switch for detecting speech signals in the presence of noise on a communication channel. The voice switch employs a threshold adjustment circuitry and three threshold detectors which include a speech detector, a noise detector and a disabling detector. The speech detector having a variable speech threshold level detects the presence of speech signals in the communication channel. The noise detector having a variable noise threshold level detects the presence of noise. The threshold adjustment circuitry, which is capable of providing rapid threshold adjustment, operates in conjunction with the noise detector to detect the noise level and to adjust the speech and noise threshold levels according to the level of the noise present in the communication channel. The disabling detector having a fixed maximum threshold level operates to disable the function of the threshold adjustment circuit while speech is present.

Abstract: An echo suppressor for use in the send path of the four-wire part of a long distance telephone circuit employs frequency-selective center clipping. The bandwidth of the channel in which echo occurs is subdivided in contiguous bands or subchannels by appropriate filtering, and each resulting signal is center clipped by a center clipper. Threshold control voltages are predicted from knowledge of the average speech amplitude distribution characteristic as a function of frequency. This characteristic is subdivided into the same frequency bands as that used by the center clippers, and the ratios of energies in the bands are used to equalize the ratios of the control voltages that determine the center clipper thresholds. This technique is implemented through the use of a peak rectifier, the input of which is coupled to the receive path of the echo suppressor and the output of which is connected to each of the filtered subchannels by a resistive dividing network.

Abstract: An echo canceller having a digital transversal filter with an adaptive control loop for achieving minimum echo is disclosed. Minimum echo is attained by subtracting a synthesized echo from the real echo, the synthesized echo being formed in a digital transversal filter by multiplying a stored replica of the impulse response times the incoming signal. The stored replica is updated using the steepest descent technique by adjusting each of the stages of the replica memory a given amount. The incoming signal is differential pulse code modulation encoded to reduce the process complexity and the size of the memories which store the replica and the incoming signals or, alternatively, increase the performance of the canceller.

Abstract: A 4 phase PSK modulator is implemented using micro-strip printed circuit technology and produces a 4 phase PSK modulated carrier by direct modulation of an RF carrier. Implementation is by means of three strip-line hybrids and two semiconductor diode phase shifters. The RF carrier is applied to one input of the first hybrid, and the other input is terminated in its characteristic impedance. The outputs of the first hybrid are connected through the semiconductor diode phase shifters to the inputs of the second hybrid. The outputs of the second hybrid are directly coupled to the inputs of the third hybrid, and the 4 phase PSK output is available from each output of the third hybrid. The semiconductor diode phase shifters are controlled to produce either 0.degree. or 180.degree. phase shifts, and by changing the state of the diode phase shifters, a separate output phase is generated for each of the four possible diode states.

Abstract: A sinewave clock distribution network and a clock driver for use in the network permit simplified distribution and synchronization in very high speed logic and digital transmission systems. The sinewave central clock is connected through a branching network to a plurality of clock drivers located in the vicinity of digital circuits to which clock pulses are to be supplied. Each clock driver includes a receiver amplifier which is AC coupled to the clock line. The output of the receiver amplifier is connected to a phase shift RC network which includes an adjustable capacitance. By adjusting the capacitance in the RC network, the timing or delay of the clock signal can be varied to permit synchronization of the clock signals at various points in the distribution network. The phase delayed signal from the RC network is coupled to a limiter which limits the input sinewave to form a squarewave for use by the digital circuits.

Abstract: An automatic H-register clear system for the prevention of erroneous convolution in adaptive digital echo cancellers is disclosed. Incoming signals from the H-register are accumulated and compared to a predetermined threshold value and when the value is exceeded, the H-register is cleared with the occurrence of the internal housekeeping cycle of the echo canceller. The clearing of the H-register allows a new impulse response model to be generated from new sampled data. In one embodiment using analog implementation, the accumulation takes place using a sequence of signal processing of digital-to-analog conversion, full wave rectification followed by integration of the signal. In another preferred embodiment using a counter detection system, each word is compared to a threshold and if this value is exceeded, a counter is indexed. If the value of the count in the counter exceeds a predetermined number during the sampling interval, the H-register is cleared.

Abstract: A digital voice switch for detecting voice PCM samples in the presence of noise samples is disclosed. The switch includes a digital variable threshold generating means which adapts the threshold level to changes in the noise level. Advantage is taken of the fact that, over a given interval of time T, speech will occur as random talk spurts separated by periods of silence, while noise (Gaussian distributed) will be continuous. This difference between speech and noise makes it possible to detect the noise level with respect to the voice switch threshold level.

Abstract: A Space Division Multiple Access (SDMA) Communications satellite system which utilizes a pair of communications satellite relays having a communications link between them. Each satellite includes a plurality of receive spotbeam antennas which are selectively connected to a plurality of transmit spotbeam antennas by an on-board switching matrix under control of an on-board oscillator. Each spotbeam antenna communicates with a different geographical zone which includes one or more earth stations. Each station may communicate with all other stations in the system including those within the field of view of the spotbeam antennas aboard the other satellite. In order to maintain synchronization between the satellites, a designated reference station transmits a reference synchronization burst of four sequential unique words to the satellite within its field of view. The reference burst is related to the other satellite and back again to the first satellite where it is relayed back to the reference station.

Abstract: Bit rate compression in a digital communications system is provided by transmitting voice information from n telephone circuits over the capacity conventionally allocated for transmission of voice information from n/2 circuits without appreciable degradation in quality. Alternatively, a doubling of the number of voice circuits may be provided with transmission at the same bit rate required for conventional digital transmission of voice information. Each frame period, at the transmitter, all n circuits are serviced and, utilizing a predictive encoding scheme, only unpredictable samples in the given frame are transmitted over the available channel capacity. A sample assignment word (SAW), which identifies the circuits corresponding to the unpredictable samples, is transmitted therewith.

Abstract: Bit rate compression in a digital communications system is provided by transmitting voice information from n telephone circuits over the capacity conventionally allocated for transmission of voice information from n/2 circuits without appreciable degradation in quality. Alternatively, a doubling of the number of voice circuits may be provided with transmission at the same bit rate required for conventional digital transmission of voice information. Each frame period, at the transmitter, all n circuits are serviced and, utilizing a predictive encoding scheme, only unpredictable samples in the given frame are transmitted over the available channel capacity. A sample assignment word (SAW), which identifies the circuits corresponding to the unpredictable samples, is transmitted therewith.