Abstract: A position system and method utilizes a plurality of range transceivers located at known fixed locations and which are adapted to transmit approximately synchronized digital range signals for receipt by both a primary receiver and a supplemental receiver, the former disposed at a known location and the latter disposed at an unknown location. The range transceivers are adapted to transmit pulse sequences which include an error portion corresponding to the approximate synchronization error of each range signal. This error portion is constantly updated in accordance with the last determined synchronization errors of the corresponding range signals received by a secondary transceiver. In an alternative embodiment employing Code Division Multiple Access (CDMA) technology, the range transceiver time stamp on transmitted range signals may be adjusted to account for the measured timing error for a given range transceiver.

Abstract: A system for marking a plurality of zones within a cellular service area. One or more marker transmitters are disposed throughout a cellular area to transmit a zone identification signal that is independent of normal RF cellular coverage to a mobile or portable cellular receiver. Each zone identification signal is transmitted in a radio frequency coverage area that illuminates the zone to be identified and is constrained by a similar transmitter jamming the zone signal. The marker transmitters are programmed to transmit the zone identification signal during a predefined time slot so that more than one marker transmitter may simultaneously transmit the zone identification signal, thereby increasing the area in which the zone identification signal can be received by the mobile unit. In order to reduce the area in which a zone identification signal may be received by a mobile unit, the marker transmitters may transmit a jamming signal at the same time as the zone identification signal is transmitted.

Abstract: An IF mixer circuit in a receiver implemented in integrated circuits employs a pair of doubly balance mixers, one injected with a local oscillator reference signal in phase while the quadrature phase of the reference signal is injected into the second mixer. A phase shift circuit adds another 90.degree. phase shift to the output of the second mixer, and the in-phase and out-of-phase signals are applied to a summing circuit to attenuate unwanted mixer products and reinforce the desired IF signal. The balanced elements of the 90.degree. phase shift circuit employ a transistor with equal emitter and collector resistances, a diode-connected transistor in series with the collector load resistance, and a collector-to-base capacitor, which provide a constant-amplitude phase shift in a unity gain structure independent of current, to produce a precise 90.degree. phase shift. Emitter current is adjustable to compensate for production variation in the absolute value of the fixed resistance, i.e.