Abstract: Disclosed is a synchronous secure communication system wherein an information signal is encrypted in an encryption means. The encrypted signal is compressed to allow the insertion of a synchronization signal, and the combined signals are transmitted. At the receiver, the synchronization signal is extracted and used to synchronize the receiver to the incoming data stream thereby improving receiver sensitivity and range.

Abstract: A method and arrangement for a fully synchronized, programmable frequency divider is disclosed that exhibits a near 50% duty cycle output signal independent of the divisor, whether even or odd, and that is suitable for use in a phase-locked loop (PLL) frequency synthesizer. As described in a first embodiment, the arrangement includes a data loader 31, a counter 32, a half-period detector 33, and a synchronizer 34. Next, a fast-locking, low-noise PLL frequency synthesizer is disclosed incorporating the fully synchronized, 50% duty cycle divider, and having a reference signal generator 71-72, a phase detector 73, a controlled oscillator 74-75, and the fully synchronized, programmable frequency divider 76. In a second embodiment, a fully synchronized programmable divider is described, including a data loader 31, a counter 32, a half-period detector 33', a synchronizer 34', and an additional block 82, a half-clock period detector.

Abstract: In a mobile communications system, a plurality of base stations may receive the same signal, whereby the "best" reception may be determined. The plurality of received digital signals are combined to form a majority signal. Each of the received digital signals is compared to the majority signal to estimate the bit-error-rate (BER) of each received signal. If the difference between the highest and lowest BER is less than a predetermined threshold, the majority signal is selected for reception. Conversely, if the BER difference is greater than the predetermined threshold, the received digital signal with the lowest BER is selected for reception. Thus, the signal with the lowest BER is selected to provide the best possible communications.

Abstract: A trunked communications system that accommodates encrypted secure communications. The system uses both non-encrypted message detectors and encrypted message detectors to assure that the trunked central control unit receives the signals it must receive in order to properly allocate and maintain channel assignments.

Abstract: A variable gain transconductance amplifier wherein complimentary input followers are used in conjunction with the multiplier to provide a high input impedance. A pair of multiplier input devices are embedded in the input followers to reduce the supply voltage used by the multiplier and to improve signal handling capability while reducing the supply voltage required. Further, these variable gain transconductance amplifiers are used in active filters to provide adjustment of the bandwidth without affecting the center frequency.

Abstract: A processing unit is provided in the form of a status and control unit which co-operates with a central station via a communications link. The unit is controlled by a microprocessor which is programmed to operate in a functional configuration controlled by the settings of one or more parameters. These parameters may be changed by means of a message transmitted to the unit from the central station.

Abstract: A vehicle mounted mobile transceiver (11) communicates via a secondary mobile unit (51) with a short range portable unit (10). The portable unit (10) can be either a cordless microphone or a transceiver. The portable unit (10) allows a remotely positioned operator to transmit messages to a base station (13). To ensure security and reliable operation, the portable and vehicle mounted units use strobe initiated digitized codes for ID and instruction purposes. These codes are newly generated from time to time by the vehicle mounted unit and are imparted to the portable unit via a battery charging interface. An improved remote squelch detect is also provided.

Abstract: A vehicle mounted mobile transceiver having a first and second frequency (11) communicates via a secondary mobile unit (51) with a short range portable unit (10). The portable unit (10) can be either a cordless microphone or a transceiver having a third and fourth frequency. The portable unit (10) allows a remotely positioned operator to transmit messages to a base station (13). To ensure security and reliable operation, the portable and vehicle mounted units use range burst signals and missed message signals to monitor receipt of data signals at the portable unit. The portable and secondary mobile unit communicate with one another via a first pair of frequencies and the vehicle mounted mobile transceiver and the base station communicate with one another via a second pair of different frequencies.

Abstract: A plurality of central stations generate and transmit control signals that are received by individual remote stations. Ordinarily, each remote station is assigned to a specific central station. The control signals include a first part that includes identifying information for one or more intended receiving stations, and a second part that includes control signals for the intended receiving station or stations. The remote stations shift operation between a first and second operating mode. In the first mode, they receive the control signals from the central station to which they are assigned, and in the second mode, they do not. For a period of time that is substantially coincident with the first part of the control signals, the remote stations operate in the first operating mode to determine whether the subsequent messages are intended for them. If they are, the remote stations continue to operate in this mode.

Abstract: An improved radio receiver that maintains a stable predetermined IF frequency upon receipt of input carrier signals of differing frequencies. The IF signal (14) is processed through a signal demodulation unit (16) that includes a tangent processing unit (22) to yield a control signal that varies as a tangent function of both the demodulated IF signal and a reference signal from a reference oscillator (17). This control signal is used to control the frequency and phase of a reference signal (26) used by the IF stage (12) to center the IF signal with respect to the IF stage characteristics.

Abstract: A zener diode random number generator circuit is described which produces a random binary number output having a statistical distribution exhibiting a controlled degree of randomness determined in response to an input control signal. A microprocessor feedback circuit monitors the random number output and produces the input control signal in response to the difference between the degree of randomness of the output signal and that of a pre-determined statistical distribution. The digital feedback automatically adjusts the zener diode biasing point and the limiter threshold such that part-to-part tolerance, component aging, temperature variations, or voltage fluctuations will not adversely affect the randomness of the bit stream output. In the preferred embodiment, the microprocessor tests the ratio of ONES bits to ZERO bits of the random number such that a desired 1:1 ONES/ZERO ratio is approximated.

Abstract: A method and means for reducing multipath interference distortion in a time-division multiple access (TDMA) communications system is disclosed. A transmitting station (100) formats one or more equalizer synchronization words with a first user's data word, time-multiplexes this formatted user message with at least one other user message, and transmits the combined signal. The receiving station (200) receives the transmitted TDMA signal, de-multiplexes the first user message from the other user messages, and equalizes the time delay spread characteristics of the data word portion of the first user message (or a stored version of such) in response to this de-multiplexing. Performing the adaptive equalization process more than once per user time slot provides an even higher data throughout for the system. Storing the first user message in a data buffer permits the adaptive equalization process to be performed in non-real time, thereby lowering the required signal processing data rate in any particular receiver.

Abstract: A speaker retaining assembly (10) that includes a support unit (12) having latches (13) disposed thereon. A retaining ring (14) functions to secure a speaker (11) in place with respect to the support unit (12). The retaining ring (14) includes an appropriately configured plurality of cavities (21) that interact with the latches (13) to so secure the speaker (11). A resilient member (36) can be utilized to bias the retaining ring (14) with respect to the latches (13) to further ensure the securement.

Abstract: In an AM stereophonic receiver a voltage is developed in response to negative overmodulation in the received signal, to detection of a pilot tone, to detection of a minimum or no signal strength condition, and to external control. Predetermined levels of this voltage are utilized to enable/disenable various function circuits within the receiver to optimize the operation.

Abstract: An EMI/RFI shield (10) comprises a box like structure formed of a metal integral member having a plurality of apertures (16) formed therethrough. The apertures (16) are of a size appropriate to substantially pass infrared energy (22) and to substantially block EMI/RFI energy (26). When placed on a substrate (18), infrared energy (22) can be utilized to reflow solder a device (19) encapsulated by the shield (10) to the substrate (18).

Abstract: FM receivers for communications at UHF frequencies often use automatic frequency control (AFS) or phase lock to precisely control a local oscillator. By causing the local oscillator to track errors and slow variations in the frequency of the received signal, these control loops suppress DC and low-frequency modulation components in the intermediate frequency signal and interfere with demodulation of low frequency information, such as digital signalling data. This invention permits recovery of the full modulation spectrum with flat frequency response. A conventional FM demodulator recovers the high frequency modulation components; the frequency control signal for the local oscillator provides the low frequency components. Combining the components with proper weighting produces recovered modulation with bandwidth limited only by the IF bandpass filter of demodulator.

Abstract: A capacitor bias unit includes a first path (26) having a first impedance (29) and a second path (27) having a low impedance and a switch (31) connected between a voltage reference source and a capacitor (23). The capacitor can either be subjected to normal charge characterisitics or quick charge by closing the switch (31). Maintaining an appropriately charged state on the capacitor (23) aids in preventing netting error voltage steps from introducing DC component signals that adversely effect proper decoding and reception of demodulated data.

Abstract: An adaptive range circuit (10) suitable for use with an analog to digital convertor (11) having operating range control inputs. The invention includes a peak detection unit (12) that can include a positive peak detector (13) and a negative peak detector (14) that provide signals representative of positive and negative peaks for the incoming analog signal to be digitized. These representative signals can be utilized to control the operating range of the A/D convertor (11).

Abstract: A trunked radio subscriber requesting dispatch service transmits a request for a channel and immediately begins to speak without waiting to receive permission to access the channel. The subscriber radio locally records the information to be transmitted and, upon being assigned a channel, begins to reproduce and transmit the information. Recording and reproduction provides delay to span the time between request for and assignment to a channel and eliminates the need for the subscriber to wait to transmit or to quickly seize a channel assigned after an initial refusal. This enhances overall response time and increases time available for transmitting information signals. During interconnect calling, a trunked system alternately assigns inbound and outbound frequencies only as required for back-and-forth communication between simplex radio and duplex wireline subscribers. Voice buffering allows the parties to begin talking during the delay between request for and assignment of frequencies.