Abstract: A proximity detector includes a low frequency magnetic field generator, located with an individual being monitored, the generator sequentially generating a plurality of encoded, time varying magnetic fields having mutually orthogonal polarizations. A magnetic field sensor unit is provided within a second device, carried by another individual. The magnetic field sensor unit is operative to detect encoded magnetic field energy associated with one or more of the magnetic fields generated by the magnetic field generator. Preferably, the magnetic field sensor unit includes a plurality of magnetic field sensors having respective magnetic field polarization sensitivities that are oriented mutually orthogonal with respect to one another.

Abstract: An antenna and method of minimizing capacitive effects of a capacitive body on a loop antenna. The antenna includes a loop antenna, a drive circuit for driving a current through the loop antenna, matching means for matching the impedance of the drive circuit and the loop antenna and a housing for carrying the loop antenna, drive circuit and matching means. The loop antenna is formed from a band of conductive material such that the flat sides of the band are normal to the plane of the loop. The loop antenna is carried by the housing when the housing is carried by a human body with its flat sides normal to the human body and its edges parallel to the human body. The orientation of the loop antenna relative to the human body minimizes the capacitive effect of the human body on the loop antenna and thus decreases the impedance to the flow of current through the loop antenna.

Abstract: A two-way communications system that provides ubiquitous wireless data communication services, such as throughout the continental United States, by using a network of only a few, widely distributed radio base station (RBS) sites and the existing paging network infrastructure. The paging network infrastructure is used as an outbound link to request data from the remote field units. The outbound page message indicates a time and HF frequency at which the RBSs can expect to receive inbound data from the field units. A network hub or mission operation center (MOC) determines a radio frequency which is expected to be propagating and clear at the time that a particular field unit is to use the frequency as an inbound link. The MOC then issues the request for data to the field unit using an existing inexpensive wireless system such as the paging network infrastructure.

Abstract: A method and system for determining whether a transmitting unit is proximate a receiving unit wherein the transmitting unit includes a magnetic field generator for a providing a plurality of time-sequential magnetic fields, each of the sequences being a differential phase shift key (DPSK) modulated code. The magnetic field is transmitted at a relatively interference free frequency of 72 KHz and the DPSK modulation frequency is about 1200 bits per second. Each pair of transmitting and receiving unit uses with a distinguishing code selected from a predetermined group of generally orthogonal codes.

Abstract: An automatic antenna tuner which conjugately matches the impedance of an electrically small antenna to the impedance of a transmit amplifier output stage by using a pi-type impedance matching network with adjustable capacitive circuit components which are preferably implemented using a low cost escapement mechanism. During an initial set up tuning procedure, a resistive Wheatstone bridge detector is disposed between the output of the power amplifier and the input to the pi network, to feedback a measure a degree of match of the pi network to a controller. The capacitive elements in the legs of the pi network are then electromechanically adjusted under the operator of the controller until an optimum setting is found. These initial impedance values are determined for each frequency in an operating range and then stored in a non-volatile memory.

Abstract: A variable capacitor and method of varying capacitance in which two pressurally engaged plates having electrically conductive patterns on facing surfaces are separated by a low friction polytetrafluoroethylene (Teflon.TM.) dielectric disk so that the plates may be rotated relative to one another to vary capacitance. Each of the facing surfaces of the plates include two spaced semicircular patterns, one that is electrically connected to the capacitor and one that is not, for maintaining the separation of the plates from the disk. The dielectric disk may be ten to twenty times thicker than the semicircular patterns.

Abstract: A system and method for isolating a data or circuit signal, where the circuit signal has been frequency spread modulated with other such signals onto a beam signal and which beam signal has been frequency spread modulated onto an IF signal, using a buss for providing the entire IF signal to a bank of frequency agile tuning demodulators. Plural IF signals may be processed simultaneously where each tuning demodulator has access to each IF signal via a plurality of IF busses. Each tuning demodulator is capable of isolating any circuit signal from any IF signal.

Abstract: A system and method for distributing plural RF signals simultaneously to many receivers. Instead of directly connecting all of the receivers by conventional cabling to the RF signals, a bus system is used. RF signals are distributed to one or more chassis each of which has one or more busses to carry each of the RF signals. Receivers may be physically and electrically removably attached to the chassis.

Abstract: A method and apparatus for improving the linearity of an analog signal in a fiber optic transmission system in which copies of the analog signal are provided to a remote receiver and to a feedback receiver, and in which the copy to the feedback receiver is attenuated so that the signal received at the feedback receiver is substantially similar to the signal received at the remoter receiver. An amplifier subtractively combines the signal from the feedback receiver and the analog signal to thereby provide a signal that pre-compensates for non-linearities that would be encountered by a transmission through the system. The feedback receiver and the remote receiver are substantially similar in operation so that the feedback loop substantially duplicates the environment of the transmission.

Abstract: A method and system for improving the linearity of an analog transmission in a multichannel fiber optic transmission system uses a power series correction derived from a non-information bearing portion of a received transmission. A notch filter reduces the energy in a portion of a guard band between channels before transmission so that the energy in the notch-filtered portion of the received transmission is indicative of the non-linearities introduced by the analog transmission system. The energy of the notch-filtered portion of a received transmission is represented by a power series that is inverted and provided as a correction to the received transmission.

Abstract: A proximity detector includes a low frequency magnetic field generator, located with an individual being monitored, the generator sequentially generating a plurality of encoded, time varying magnetic fields having mutually orthogonal polarizations. A magnetic field sensor unit is provided within a second device, carried by another individual. The magnetic field sensor unit is operative to detect encoded magnetic field energy associated with one or more of the magnetic fields generated by the magnetic field generator. Preferably, the magnetic field sensor unit includes a plurality of magnetic field sensors having respective magnetic field polarization sensitivities that are oriented mutually orthogonal with respect to one another.

Abstract: A sealed semiconductor unit includes an electrical component within a defined area on a semiconductor material. A cover with the dimensions of the semiconductor defined area is placed over the semiconductor material with a sealant there between. The dimensions of the cover are aligned with the dimensions of the semiconductor. The sealed unit includes electrical contacts extending from outside the sealed unit to the electrical component within the sealed unit on the semiconductor material. The sealed semiconductor unit, including the cover, the semiconductor material, and the electrical component, has an area of the semiconductor material.

Abstract: An amplifier circuit employs a differential amplifier having first and second differential inputs and having an output for providing an output signal which varies according to a difference between magnitudes of input signals provided at the first and second inputs, a high impedance front end which is coupled to the first input of said differential amplifier and which accepts an input voltage, and a feedback circuit which is interposed between the second input and the output of the differential amplifier so that error characteristics of the feedback circuit are substantially similar to error characteristics of the front end and signal errors introduced by the high impedance front end are canceled by signal errors provided by the feedback circuit. The differential amplifier can be an operational amplifier and the high impedance front ends and the feedback circuits can be source follower FET circuits each having an FET transistor and a resistor connected to the source terminal of said FET transistor.

Abstract: Analog (LC) circuit components for an input matching and base charge removal network for a Class-C amplifier are replaced by a digitally driven shunt circuit, which is coupled between the base electrode of the Class-C power transistor and a reference voltage terminal (ground). The digitally driven shunt circuit is operative to couple the base electrode of the power transistor to the reference voltage terminal upon the termination of the limited duty cycle input pulse employed as the base drive to the power amplifier. To facilitate implementation as a digital application specific integrated circuit (ASIC), the controlled shunt circuit comprises an auxiliary or second bipolar transistor having its emitter-collector path coupled in circuit with the base of the bipolar power transistor and the reference voltage terminal.

Abstract: The gain of a recursive integrator is controlled so as to be adaptive to the quality of a received signal by comparing the magnitude of its emphasized information component with a reference voltage and controlling the gain of the integrator's feedback delay path in accordance with the difference between the peak value of the emphasized information component and the reference voltage. As a result, when the signal to noise ratio of the input signal is high, the gain can be reduced, so that the recursive loop will adapt quickly to changes in a multipath profile.

Abstract: A broadband, high-gain RF signal amplifier which consumes a minimal amount of DC power has an input terminal to which an input signal to be amplified is coupled, and an output terminal from which an amplified output signal is derived. The signal amplifier has a plurality of first through n.sup.th signal amplification stages coupled in cascade between the input terminal and the output terminal. Each stage comprises an amplifier device having an input electrode, an output electrode and a control electrode. The output electrode is coupled to an amplifier device of an i.sup.th stage that is resistively coupled to the input electrode of the amplifier device of an (i+1).sup.th stage, and is DC coupled through a rectifier device to the control electrode of the amplifier device of the (i+1).sup.th stage. The control electrode of the amplifier device of the i.sup.th stage is resistively coupled to the input electrode of the amplifier device of the (i+1).sup.th stage.

Abstract: A hybrid despread and demodulation receiver for low symbol rate communications employs a passive (SAW) matched filter to remove a "short" coding portion of a composite spreading code that has been used to spread the data signal. The composite spreading sequence is formed by multiplying different length coding sequences, thereby obtaining an overall signal processing operator the duration or symbol span of which is sufficient to maintain a high signal processing gain, but is considerably longer than can be processed using a practical sized passive (e.g. SAW) filter design. The design of the receiver takes advantage of the fact that the relatively short sequence can be despread using a practical SAW structure and is comprised of a hybrid signal processor, the front end of which contains a compact SAW matched filter and the downstream end of which is implemented using analog processing components.

Abstract: A monolithic FET bridge attenuator contains four single gate FETs, the source-drain path of each of which forms a respective arm of the bridge. The attenuation control electrodes (gates) of the FETs in opposite arms of the bridge are connected to a common control voltage. A first pair of diagonally opposing nodes of the bridge are coupled to receive respective input signals that differ in phase by 180.degree.. A second pair of diagonally opposing nodes of the bridge disposed between the first pair of nodes provide a pair of output signals differing in phase by 180.degree.. In effect, each FET has the electrical behavior of a parallel RC circuit, the resistive component of which is controlled by the gate voltage.

Abstract: A dual gate MESFET attenuator circuit provides substantial range of attenuation without phase shift through a cascaded arrangement of a pair of dual gate MESFETs and the incorporation of a feed forward resistor. By cascading the two transistors together, the attenuation vector characteristics are effectively rotated 180.degree. or shifted to the third and fourth quadrants of the (real/imaginary) vector plane. The resulting phase shift between the minimum attenuation vector and the maximum attenuation vector is compensated by the insertion of a pure resistance component in a feed forward fashion between the input and output terminals of the cascaded dual MESFET pair. The value of the inserted resistor is chosen so as to effectively make both the maximum attenuation vector and the minimum attenuation vector cophasal, thereby providing a constant phase shift through the attenuator over a substantial range of attenuation.

Abstract: A microwave transistor circuit includes a pair of field effect transistors connected in cascade via a standard 50 ohm transmission line having a length equal to one-half the wavelength of the operating frequency range of the circuit. Although the field effect transistors are individually unstable at microwave frequencies, by cascading these transistors the reverse transmission coefficient is sufficiently reduced to render the overall circuit unconditionally stable. In addition, the transmission line is opened to provide physical isolation between the transistors for d.c. bias isolation and a capacitor is connected therein to provide for RF continuity.