Abstract: A driver for driving the anode of a laser diode includes a constant-current differential switch comprising NPN transistors. Two sources supply constant current into the node where the differential switch drives the laser diode: one source supplies bias current through the laser diode; the second provides a current substantially equal to the constant current through the differential switch. When the transistor, which drives the laser diode, is turned on by a modulating signal applied to its base electrode, the current from the second source flows through it into the current source at the common emitter junction. When this transistor is turned off, the current from the second source flows through the laser diode, adding to the bias current therethrough. Under these circumstances, the total current through the laser diode exceeds the threshold for lasing action and the laser diode is turned on.

Abstract: In a wave soldering apparatus including a station for forming a standing wave of foamed flux, a preheater station, and a standing wave of hot molten solder station, a flux removing apparatus for reducing the thickness of flux on a coated printed circuit board includes an apertured pipe for gently blowing a plurality of streams of air against the foam coated board, the streams acting effectively as a continuous linear stream of air. The airstreams also blow the foamed flux into apertures in the printed circuit board.

Abstract: A voltage regulator for controlling the voltage of a bus powered by N solar cell arrays. Digital shunts are coupled to N-1 of the arrays. A linear shunt is coupled to the remaining array. Current passing through the remaining array is sensed by the linear shunt which, in response thereto, turns on and off various ones of the digital shunts to maintain the desired voltage on the bus.

Abstract: A security system is disclosed which senses a variety of activities which affect a secured area and/or the boundary which defines it and identifies particular activities rather than merely indicating that some activity is present. A transducer comprising an electroded ferroelectric film of polyvinylidene fluoride (PVDF) serves as a transducer which provides different output signals in response to different stimuli and responds simultaneously to thermal and mechanical activity. A signal processor separately recognizes the signals produced in response to different activities and identifies the activities detected. An alarm processor controls the system and generates alarm signals in response to the detection of specific activities.

Abstract: A low-friction slide apparatus for use with the translation stage of an optical disc recording/playback system is disclosed. The apparatus includes a rail which is fixed in position. The rail includes porous strips affixed to two orthogonal sides along its longitudinal dimension. A plurality of passages between the rail and the porous strips permits air to be forced outwardly through the pores of the strip material. The slide member, which is movably mounted on the rail, has bearing surfaces adjacent the porous strips attached to the rail. Permanent magnets mounted along these bearing surfaces maintain an attractive force between the slide and the rail, countering the force direction of the air flow, thus providing a low-friction bearing film of compressed air. A linear motor included in the rail and slide member induces motion of the slide along the rail.

Abstract: An arrangement for coarse and vernier measuring of the delay or phase shift introduced by a delay path by generating a recurrent pseudorandom signal at an original chip clock rate derived from a reference clock. At the receiving end of the delay path, a delay locked loop regenerates the chip clock and the pseudorandom signal at a phase established by the delay. The coarse count is measured by the number of chip clock cycles. The vernier delay is measured in terms of a fractional portion of a chip clock cycle. The vernier measurement is made by starting a counter which counts reference clock signals in response to a coincidence of the original chip clock and the reference clock, and by ending counting and latching the count in response to coincidence of the regenerated chip clock and the reference clock.

Abstract: Two or more distributed amplifiers are paralleled to increase the available output power. Phase shifters are coupled to the amplifiers as necessary to maximize output power at a frequency. With this phase adjustment, the amplifiers may have effective electrical lengths which differ one from another by N (360.degree.), where N is zero or an integer. Values of N other than zero undesirably reduce the instantaneous bandwidth of the paralleled amplifiers. The bandwidth is maximized by the addition of sufficient delays to reduce N to zero.

Abstract: A magneto-optic disc recording system includes an E-shaped electromagnet for providing magnetic biasing selectively for the recording and erasing processes. The middle arm of the E comprises a first pole piece and is positioned radially with respect to the disc rotation, on the opposite side of the disc from, but aligned with, the path of radial motion of the focused recording/erasing light beam. The other arms of the E, parallel to the middle arm, comprise second pole pieces opposite in polarity from the first pole piece, and are positioned adjacent the disc recording surface on the opposite side of the disc from the middle arm. Two shoes of a magnetic material, coupled to the optical translation stage, provide a magnetic circuit between the respective second pole pieces and the area surrounding the objective lens focusing light on the disc recording surface, relaying a substantially vertical magnetic field through the disc at the point of incidence of the focused light beam.

Abstract: A magneto-optic disc recording system includes a cylindrical permanent magnet for providing magnetic biasing selectively for the recording and erasing processes. The magnet is positioned radially with respect to the disc rotation, on the opposite side of the disc from, but aligned with, the path of radial motion of the focused recording/erasing light beam. The poles of the magnet are diametrically opposed, and the magnet is axially rotatable. Circular eddy currents, induced by the magnetic field of the magnet on the surface of the rotating disc, generate a second magnetic field which opposes the field of the magnet, thus impelling rotation of the magnet. A stopping mechanism stops the rotation of the magnet with one or the other of its poles adjacent the disc, such that either a recording or erasing magnetic bias is selectively provided to the recording region.

Abstract: A closed-loop, temperature-controlled cooling system includes a Stirling cycle refrigerator driven by a dc motor, wherein the motor excitation derives from pulse width modulation. Temperature control of the cooling system is provided by a temperature-sensitive bridge circuit which responds to variations in temperature by generating an error voltage which effects a change in the modulator duty cycle. The amount of cooling is directly related to the average voltage applied to the motor, which is a function of the modulator duty cycle and the amplitude of the supply voltage. A compensation circuit is disclosed which responds to variations in the voltage amplitude of an unregulated supply by coupling an error signal to the bridge circuit to thereby affect the modulator duty cycle.

Abstract: A reduced size and weight beam forming network for a circularly polarized N element array antenna system is achieved by interconnecting quadrature couplers without intermediate phase shifters and adding twisted waveguide phase shifters at the coupler outputs to equalize the phase at the array elements.

Abstract: A digital filter system in which the frequency spectrum of an input signal is divided into M consecutive subbands. Each subband is generated by multiplying the impulse reponse of a low pass filter by a sinusoid (sine or cosine) whose frequency is equal to the center frequency of its respective subband. The sinusoids of adjacent bands are phase shifted by 90.degree. relative to each other to establish a condition enabling aliasing components to be cancelled when the subbands are recombined.

Abstract: A DC-to-AC inverter includes a switched bridge circuit. The bridge is energized by a source of substantially constant direct current. In order to reduce stress on the switches of the bridge, periods of conductivity of the switches of the bridge are overlapped, so that all the legs of the bridge are conductive simultaneously in two operating intervals out of a recurrent operating sequence of four operating intervals. Each switch is associated with a snubber circuit including a snubber capacitor which bypasses or absorbs switch current during turn-off. The charge retained on the snubber capacitor after complete turn-off of the associated switch represents energy which can be reused. The capacitor must be discharged in readiness for the next turn-off of the associated switch.

Abstract: An adaptive carrier tracking circuit for receiving pulse code modulated communications which have passed through a scintillation environment is disclosed. The rate and magnitude of phase or frequency fluctuations of the input signal are detected and the bandwidth of a circuit filter is adjusted in response to an estimated decorrelation time to optimize the signal tracking and bit error rate for the circuit. The adaptive carrier tracking circuit may be applied to communication systems tracking circuits utilizing phase-locked loops or modified Costas loops for phase tracking, or automatic frequency control loops for frequency tracking.

Abstract: A reflector antenna system with reduced blockage effects is provided by placing a compensating reflector between the surface of the main curved reflector and its primary feed to intercept illuminating radiation which would otherwise be blocked by the feed. The compensating reflector reflects the intercepted radiation with a beam pattern which is essentially identical to the substractive blockage pattern. The compensating reflector is spaced from the main reflecting surface to place its beam pattern in phase opposition to the blockage pattern to cancel common components from the blockage pattern.

Abstract: Messages sent from an earth station to a satellite by a command link are authenticated within the satellite before being executed. Authentication is accomplished by comparing a codeword appended to the message to a codeword generated within the satellite. This codeword is a cryptographic function of the message data and a secret operating key. A key change command from the earth station causes the satellite authenticator to generate a new operating key based a secret master key, a supplemental private code, and a publicly available initialization vector. The codeword appended to the key change command is encrypted in the new key and, if it agrees with a codeword generated by the satellite authenticator, the new key becomes the operating key and the key change function is complete.

Abstract: A subsurface antenna system including at least one pair of radiating elements and feed system is buried within a subsurface medium. The radiating elements comprising the system are spaced apart at least one quarter free space wavelength at an operating frequency. The radiating elements are spaced from each other and the feed system provides appropriate relative phase to signals at the elements to produce from the antenna system a directional antenna pattern in free space.

Abstract: An antenna reflector comprising a face skin of graphite fiber reinforced epoxy (GFRE) material is coated with a layer of chromium. The chromium is then coated with aluminum and a protective coating of silicon dioxide is then deposited over the aluminum. The chromium has a thickness sufficiently thin to provide good coverage of the pores of the GFRE material and to minimize distortion causing poor bond due to differences in the coefficient of thermal expansion of the different materials in the presence of temperature cycles. The aluminum is sufficiently thick to provide good reflecting characteristics to minimize the polarizing effects of the graphite face skins.

Abstract: A solar array panel is formed of a matrix of solar cell subarrays and wired together to form an integral power unit. The subarrays are soldered by passing them on a conveyor through successive solder melting and solder cooling regions induced by suspended radiating susceptors which are inductively heated. The system induction generator is cycled on and off to create the desired temperature ranges in the applicable regions. The subarrays are carried through the regions by an aluminum alloy plate on a thermally inert conveyor belt. The aluminum alloy plate is substantially unresponsive to radiated heat from the susceptors.

Abstract: A constant-current, current-programmed dc-to-dc converter includes a controllable switch and an inductor. The switch is rendered conductive in response to a recurrent clock signal, and nonconductive in response to a comparison of a voltage representing the inductor ramp current with an output voltage error signal from a high impedance source, which establishes an output voltage control feedback loop. An overcurrent limiting circuit includes a current sensor having a low output impedance which produces a load current representative signal. The load current representative signal is applied to an amplifier having a low output impedance and which includes a diode in its feedback loop to maintain it nonsaturated. A second diode is connected to the output of the amplifier and to the high impedance output terminal of the error voltage source to close a current limiting degenerative feedback loop which swamps the error voltage when the second diode becomes conductive due to excess load current.