Abstract: An automatic gain control (AGC) method and circuit (10) within a receiver uses a digital state machine (26) to implement the AGC function. independent from interaction with a host processor (36) and for multiple modulation protocols without duplicating circuitry. Modulation protocol and parameters for any of various gain responses are stored in a register (29). Multiple states, each corresponding to a predetermined range of RF input signal strength, are stored in the register. Each state contains parameters that determine a gain control signal for controlling a variable gain amplifier (16). The states are independent and may be selectively disabled to create asymmetric responses. Within any state, an adaptable number of iterations may be set to implement a different update rate or step size after a predetermined number of closed loop gain change iterations has not resulted in a transition to a state that represents a desired output gain.

Abstract: A location determination device (104) is worn on a user's head to facilitate searching and tracking for another individual carrying a portable radio (102) as well as locating exit routes. At least two antennas (108), a monopulse receiver (110) and a display are integrated into the location determination device (104). Location determination device (104) scans for an incoming signal (106) from the portable device (102) and coverts the signal into angular location data. The location data and egress information are displayed to the peripheral vision of the user of the location determination device (104).

Abstract: An adaptive dc compensation technique (100) eliminates dc error for both digital and constant envelope modulation protocols (108). For analog modulation, a dc averaging technique utilizes piece-wise continuous dc averaging (110) that calculates discrete dc error values over a variable number of samples (112) and updates the dc compensation value as a fixed value for a specified sample length (114). The piece-wise “update-and-hold” technique (110) results in a pseudo high pass filter response with an equivalent corner. For digital modulation, a continuous high pass filter section of the receiver is enabled (120).

Abstract: A system for integrating environmental sensors and asynchronous ubication repeaters forming an n-point spatially random virtual lattice network (100) includes a ubication repeater (101) for communicating both positional and environmental information to a two-way radio transceiver (102) used by police or firefighters. The ubication repeater (101) initially determines its position upon actuation from the two-way radio transceiver (102) where environmental information can be transmitted to the firefighter's two-way radio transceiver (102) or to a central location (104). The central location (102) can provide a composite overview of an environmental situation during an emergency.

Abstract: A receiver direct current offset correction loop (DCOCL) circuit digitizes the baseband analog control voltage (148) using an Analog-to-Digital Converter (ADC) block 160, which is then processed at control block (162) to drive compensation circuitry 164 in a classic feedback configuration. The DCOCL is augmented by an independent automatic gain control (AGC) circuit that utilizes the same control signal (148). The AGC circuit includes a multiplicity of adjustable gain stages (114, 118, 158) with threshold and characteristic response that is controlled by AGC control block (122). Both the AGC and DCOCL circuits are dynamically configured for optimum complimentary operation via the microprocessor (236) depending on the receiver's operating environment and protocol requirements. Subsequent direct current (DC) voltage drift is detected by the digital signal processor (DSP) block (230) which in turn flags the microprocessor to reinitiate the correction sequence when needed.

Abstract: A SONAD (110) control system (100) detects a received signal strength (RSSI) for a radio frequency (RF) signal (102), selects a threshold transfer function (400-404) in response thereto, generates a threshold control signal in response to the transfer function, and utilizes the threshold control signal to select the SONAD threshold value. During operation, the control system (100) decreases the attenuation of background noise levels for weak RF signals.

Abstract: A multi-layered coupling device (FIG. 9) for coupling radio frequency (RF) energy on a transmission line (302) to a coplanar coupler. The coupling device includes a first coupling structure that is coplanar with the transmission line (302) and parallel plate structure (304) positioned a predetermined distance in a plane parallel to the transmission line (302). The parallel plate structure (304) is not physically connected to any other structure through the use of vias or the like. The parallel plate structure (304) is used to increase the coupling coefficient and directivity of the coplanar structure by being divided into a plurality of segments with varying dimensions to better control coupling capacitances.

Abstract: A coupling device (100) for coupling RF energy on a transmission line (101) to a forward coupler (107) and a reverse coupler (113). The coupling device (100) includes a first coupling structure (121) and second coupling structure (125) which are parallel plate structures positioned a predetermined distance in a plane parallel to the transmission line (101), forward coupler (107) and reverse coupler (113). The first coupling structure (121) and second coupling structure (125) are used to increase the coupling coefficient and directivity of the forward coupler (107) and reverse coupler (113). One or more vias (139, 141) are used to connect forward coupler (107) and reverse coupler (113) to the first coupling structure (121) and the second coupling structure (125). The addition of the first coupling structure (121) and the second coupling structure (125) allow for a greater coupling efficiency without physically moving transmission line (101) towards either forward coupler (107) or reverse coupler (113).

Abstract: A tunable filter (100) includes first and second resonant structures (140, 145) coupled by a capacitive coupler (120). The capacitive coupler (120) includes two tunable elements (121, 126) coupled by a capacitive circuit formed at least in part by a capacitive pi-network (130).

Abstract: A radio receiver (10) comprises a plurality of stages and means for selectively adjusting the stages (16, 18, and 22), as a function of the received signal strength to reduce intermodulation distortion. In still another aspect of the invention, a receiver determines the signal strength of a received signal and uses this information to selectively control stages of the receiver in order to reduce the receiver's current drain.

Abstract: A receiver (100) includes an audio section (200) which provides for compensated squelch settings which are automatically adjustable for changes in operating conditions such as changes in temperature or receiver channel spacing. Temperature circuit (128) provides a temperature signal (134) and controller (122) provides a signal indicating the channel spacing being used by receiver (100). The two signals are combined and formed into an address word which is in turn used to look-up a compensation word from memory location (218). The compensation word is then combined to a default squelch word by adder (216) providing for a compensated squelch word. The compensated squelch word automatically adjusts the squelch circuit's threshold level in order to compensate for changes in operational conditions affecting the squelch circuit.

Abstract: A crystal filter network comprises at least one variable impedance network (103a, 103b), at least one crystal filter (103c), and a control circuit (110). Each variable impedance network (103a, 103b) has a control terminal, a first terminal (37, 39), and a second terminal (38, 40) for connecting a first impedance (113) coupled to the first terminal (37), to a second impedance coupled to the second terminal (38). The crystal filter (103c) is coupled to at least one of the first and second terminals. Coupled to the control terminal, the control circuit (110) electrically varies (V.sub.1 and V.sub.2) the variable impedance network (103a, 103b) to provide a predetermined impedance characteristic to the crystal filter network (103c).