Abstract: A multi-filter device comprising a ceramic block (10) having at least two filters A and B. Both filters A and B include a notch (11 and 13, respectively) formed on one side of the ceramic block (10), such that these notches are flanked by ceramic block material extensions (32). So configured, coarse tuning of the ceramic block (10) can be accomplished through use of existing double-sided lap techniques, yet constant parameter alteration for both filters will be maintained during the milling process.

Abstract: A method to implement multiple talk-around communication links using the communication resources of one repeater. A system resource controller determines whether talk-around is possible for any two communication units intending to engage in a point-to-point communication link. Assignment of a talk-around repeater depends on the geographic locations of the two communication units, and a predetermined range criterion between them. In addition, the talk-around communication must not interfere with any existing talk-around communication already in the system. When talk-around communication is possible, an enabling communication grant is issued to the units, and the talk-around repeater's communication resources are assigned to support the link. Otherwise, a repeater for normal trunking is assigned.

Abstract: A channel allocation mechanism especially useful in a trunked communication system that can accommodate both voice and data signals, and that operates in true trunked manner to efficiently utilize spectral resources.

Abstract: Variable hangover time is provided for a speech coder (105). Voice activity within a speech message is detected (209) using a voice activity detector (VAD) (107), and a signal-to-noise ratio is calculated. A variable hangover time is calculated (215) and appended to the time in which voice activity is detected, producing an extended voice detection period. The speech coder (105) is enabled only during the extended voice detection period, thus saving power.

Abstract: A subscriber unit for use with a duplex communication system is described. The present invention contemplates a duplex transceiver which incorporates data and voice handling capability. A microprocessor generates data and DTMF signaling as well as decoding received data. According to the principles of the present invention, an improved duplex capable subscriber unit is achieved by coupling a microprocessor to a duplex transceiver through switchable filters. The filters exhibit a relatively fast or slow time constant depending on the state of a filter control input. The microprocessor is then capable of operating the subscriber unit with optimum frequency response characteristics depending on whether voice or data is being received. In addition, a summing network coupled between the microprocessor and the transmit switchable filter cooperates with the switchable filter and allows the duplex subscriber unit of the present invention to generate DTMF signaling.

Abstract: A key management system for encryption keys removes the effect of secure communications loss during a rekey period in a secure communications system. Use of key indexes to partition encryption keys into usable subgroups such that during a rekey period, continuous secure communications are maintained throughout the entire secure communications system.

Abstract: In a trunked communication system using intelligent repeaters (101), each intelligent repeater performs a series of tests (602, 606, 610, 614, and 618) on its own functionality. The results of these tests are transmitted (622) to a resource manager, which is one of the intelligent repeaters at a communications site. Using the results of these tests, the resource manager then selects one or more of the intelligent repeaters to perform the functions of authorization, resource allocation (708), and logging of communications (713).

Abstract: An analog signal having an input level is provided. The analog signal is converted into a digitized representation of the analog signal in an analog to digital converter (105) that uses an operating range. The digitized representation of the analog signal is processed (107) to determine the input level for the analog signal. The input level for the analog signal is compared (109) with a reference signal to provide a comparison signal. The comparison signal is manipulated (111) to adjust the operating range.

Abstract: A transceiver compatible with both wide channel constant envelope 4 level FSK FM modulation and narrow channel .pi./4 differential QPSK linear modulation allows compatible interaction between modified constant envelope and non-constant envelope transmitters. All Nyquist filtering occurs in the transmitters, and none in the receiver.

Abstract: A heat sinking apparatus that dissipates heat generated by a surface mountable power device, which can be auto picked and placed, comprises a first planar surface, at least one gull wing mounting tab, and at least one connective leg. The at least one connective leg thermally couples the first planar surface to the gull wing tab and all three structures are comprised of a thermally conductive material. When the heat sinking apparatus is coupled to a substrate, heat generated by the surface mountable power device is thermally transferred through a thermal plane of the substrate to the heat sinking apparatus.

Abstract: A wireless binary coded optical data receiver receives the binary encoded data via a photodiode. The binary encoded data is then supplied to the primary winding of a transformer and thus coupled to the secondary winding of the transformer. The secondary winding is coupled to a transimpedance amplifier wherein the transimpedance amplifier buffers the received binary encoded data. The buffered binary encoded data is then amplitude limited by a limiting circuit.

Abstract: A master repeater controls a trunked communication system having a number of communication resources. The master repeater determines (201) how many communication resources are available to the master repeater. When one control resource and one message resource are among the available communication resources (203), the master repeater suspends (211) trunked communication system operation when the number of available communication resources are less than a minimum number of resources (205), and the available communication resources fail to include all control resources (207) from the trunked communication system.

Abstract: In a system where 2-level modulation and 4-level modulation of communication signals exist, an apparatus (107) demodulates either modulation scheme by demodulating (301) a received signal under the presumption that it is a 4-level signal, and if the received signal is detected (309) to be a 2-level signal, the signal is then demodulated (319) as a 2-level signal.

Abstract: Simultaneously detecting both frame and bit synchronization in a serial bit stream reduces the time required to have a receiver lock up to a transmitted serial data signal. A dual-phase correlator circuit is used to detect frame synchronization while a multiphase commutator circuit detects bit clock synchronization.

Abstract: In a radio communications system, a selectively enabled time- and/or frequency-diverse signaling scheme is employed to improve signal quality. In particular, a method of exchanging a message between communication devices using a communications resource might include the step of transmitting a first portion of the message on a first frequency within the communications resource. After determining the quality of the communications resource to be unfavorable, a second portion of the message might be transmitted on the first frequency, and also re-transmitted on a second frequency and/or at a separate time.

Abstract: An operator MUX interface (OMI) (102) includes a data base manager (203) that manages at least two data bases. The first comprises a substantially non-temporary data base, and the second comprises a substantially temporary data base. The latter includes information from both the first data base, and other information as well. The data base manager (203) automatically alters the data storage structure of the second data base whenever either the data storage structure for the first data base is changed, or whenever new information must be added to the second data base, and the data storage structure of the second data base will not readily accommodate that addition.

Abstract: Adaptive digital coding of received analog information based on signal strength can be accomplished in the following manner. Once a repeater receives analog information from a communication unit, the signal quality of the received analog information is determined. Next the signal quality of the received analog information is compared with a first signal quality value. If the signal quality of the received analog information is above the first signal quality value, the received analog information is digitally coded based on a first digital coding format. If the signal quality of the received analog information is below the first signal quality value, the received analog information is digitally coded based on a second digital coding format.