Abstract: An LED and battery powered driver circuit provide efficient operation to conserve battery energy and maintain the intensity of light emitted from the LED at a substantially constant level despite changes in the battery voltage due to charging and discharging. A pulsed voltage output of a switching power supply is capacitively coupled to the LED. The voltage amplitude of the output pulses is maintained substantially constant by a duty cycle modulator which is connected in a feedback path of the switching power supply. A diode or a transistor circuit is provided to discharge the capacitor between voltage pulses.

Abstract: A dispatch trunked radio system which provides duplex or simplex telephone interconnect communications to subscriber units is described. The system allows duplex capable trunked system subscriber units to establish a full duplex communication link with conventional land based telephone interconnect service in accordance with a method which unifies the operation of the trunked system subscriber units, a plurality of trunked system repeaters, a trunked system central control unit, and a telephone interconnect control unit. The method of the present invention also provides improved trunked system performance by allowing simultaneous transmission and reception of channel controlling information.

Abstract: An I.sup.2 L programmable read only memory (PROM) output circuit has a selectable dual non-inverting input differential amplifier with each non-inverting input connected to a different column of memory elements. In the read mode the circuit operates at very low power levels and down to 1 volt. To program the memory elements, the circuit includes two selectable programming current sources which self extinguish as soon as the memory element being programmed changes from its unprogrammed to its programmed state. Switching between the read and program modes is accomplished merely by changing the voltage on the B+ terminal; 1-3 volts for read and 9-12 volts for program.

Abstract: An alphanumeric entry system which is provided with an electronic lock-out feature. The keypad entry system of the present invention comprises an alphanumeric keypad having function keys and display, a microprocessor, and an electronically programmable read-only memory device. The display consists of a series of system related menus as well as an alphanumeric display area. One of the system related menus corresponds to a locking feature, which may be activated by a general purpose function key. In the locking mode, the radio keypad toggles between a locked and unlocked condition as controlled by the function keys in accordance with a predefined sequence. The alphanumeric entry system of the present invention is particularly advantageous for use with portable two-way communications equipment which operate in a plurality of radio systems.

Abstract: A portable radio transceiver and mobile mount housing are disclosed which utilize a switchless connector for connecting the portable unit to an external antenna which is electrically coupled to the mobile mount. In the preferred embodiment, the portable radio is equipped with an internal antenna which is either coupled to an electrical contact on the exterior of the portable unit adaptable to making electrical contact with a similar contact on the inside of the mobile housing when the portable radio is inserted therein. The internal antenna in the portable unit is shielded by the metallic mobile mount housing which obviates the need to disconnect the same. In one embodiment the contact disposed on the portable unit exterior is connected to a predetermined point on the internal antenna for impedance matching with the external antenna when the portable unit is inserted into the mobile mount housing.

Abstract: A switched capacitor filter system is provided which is programmed to filter a predetermined sequence of tone signals. The filter system is de-rung after each selected tone signal is detected by increasing the clock frequency of the switched capacitor from the programmed value corresponding to a tone signal up to a center frequency substantially greater than that of the tone signals. Energy stored in the filter system is thus quickly dissipated. Rapid sequences of sequential tone signals are thus filtered without the problems associated with ringing of the filter.

Abstract: A reduced power consumption low battery indicator comprising in the preferred embodiment a transducer driver which drives a transducer to provide an audible alert. A microprocessor is used to generate a squarewave signal to power the transducer driver whenever the battery is depleted to a first predetermined level. A first low battery sensor is used to determine when the battery is depleted to the first predetermined level and generates a signal which is directed to the microprocessor to commence generation of the signal to drive the transducer driver. A second low battery sensor is used to determine when the battery is depleted to a second predetermined level and generates an output signal which is directed to the transducer driver which then drives the transducer at a lower power consumption rate.

Abstract: A pocket clip suitable for attaching a personal paging receiver to an article of clothing has an integral character display. The pocket clip has a rigid lower housing part, and a plastic upper housing part containing the display and a circuit board with display decoder/driver circuitry. A conductive elastomer electrically connects the circuit board to the display while a flex circuit connects the circuit board to the paper. Bayonet tabs on the lower housing mate with slots in the upper housing to slideably connect the upper and lower housing parts. In one embodiment, the pressure necessary to clamp an article of clothing between the pocket clip and the pager is generated by a pawl, pivotally attached to the clip, with compressed springs positioned between the pawl and the clip. In another embodiment, the clamping pressure is generated by a torsion spring. An optional integral switch is also described.

Abstract: A radio paging test system for testing the sensitivity of a radio receiver which receives a group of transmitted signals from a transmitter. Each transmitted signal in the group of transmitted signals is detected ad then compared to a reference signal to determine the degree of similarity between the reference signal and the detected signal. Each detected signal is classified either as a missed page, a non-page or a decoded page depending on the degree of similarity between the detected signal and the reference signal. In one mode of operation the classification of each detected signal is indicated by a classification signal which may be utilized to activate an alert such as a transducer or LED. Each classification signal may be directed to a computer input for analysis. In another mode of operation the classification signals are further analyzed to determine if the pager sensitivity is above, below or at a predetermined level. An alert indicating the pager sensitivity is then generated.

Abstract: A rechargeable high energy density cell having a metal--metal oxide negative electrode, more specifically, the metal being cadmium, wherein the metal is in the form of thin flakes. Such cells show improved energy density and cycle life when charged-discharged at higher rate and to 100% depth of discharge.

Abstract: In a method of electrically altering the characteristics of a semiconductor device, a lateral polysilicon zener diode's zener knee voltage may be shifted either to a higher or lower voltage. An electrical potential may be applied in the forward direction to shift the zener knee to a higher voltage level. An electrical potential may be applied in the reverse bias direction to shift the zener knee to a lower voltage. In the limit, the zener may be changed into a forward diode of reverse polarity with respect to the original zener. The electrical potential used should be of appropriate magnitude to melt the polysilicon without damage to the zener's terminals. This induces migration of the impurities causing a rediffusion of impurities thereby altering the characteristics of the diode. This method may be used to program a PROM by either converting the zener to a diode or not to program each binary bit.

Abstract: A power supply circuit includes a battery power source connected by a switch to the input of a DC to DC converter. The output of the DC to DC converter is connected to a filter capacitor and a load. A crow-bar is connected to the input and the output of the DC to DC converter. The crow-bar shorts the output to ground to discharge the capacitor when the voltage at the input drops to a predetermined value.

Abstract: An adaptive impedance mismatch detector system is provided for determining whether or not a particular load impedance is matched or mismatched to the characteristic impedance of a transmission line. The detector system is capable of determining if a particular load impedance has a value outside of an impedance threshold circle having a center at a location other than at the center of the Smith Chart. The system changes the radius and/or center of the threshold circle in response to changes in circuit operating conditions or parameters. This flexibility enables the detector to be more selective in determining improper load conditions.

Abstract: The present invention in the preferred embodiment comprises a plurality of current mirror circuit stages connected together for amplifying a first input signal and generating an output signal. A shunt path circuit is connected to the first stage of the plurality of current mirror stages and when activated by a second input signal shunts a portion of the first input signal to ground, thus reducing the current flow into the plurality of current mirror stages. During normal operation, when the shunt path circuit is inactivated, the last stage of the plurality of current mirror stages functions as a switch and passes all of the amplified first input signal. However, during the low power consumption mode, when the shunt path circuit is activated, the last stage of the plurality of current mirror circuit stages functions as a current mirror circuit and passes current at a considerably reduced level.

Abstract: A radio transceiver includes a read only memory (ROM) for storing an origination code and a random access memory (RAM) for storing a destination code. The destination code may be manually entered into the RAM via a keypad or it may be entered remotely from another transceiver. In signalling between two transceivers, the destination code is transmitted followed by the origination code indicating the transmission's origin. In this manner coded squelch communications may take place between two parties without the necessity of reverting to carrier squelch operation while obtaining enhanced user privacy and flexibility.

Abstract: In a data message communication system, certain messages require a return acknowledgement signal. The present invention contemplates a method and means which are activated whenever an outbound message is received. Each portable unit which receives a message then monitors the outbound communication channel to determine if the inhibit signal is currently active. If the inhibit is not currently active, the particular unit will transmit its acknowledgement message immediately. If the inhibit signal is active, each portable unit will maintain a count of the number of outbound messages, addressed to other units requiring an acknowledgement, since that particular portable received its message. At the termination of the inhibit signal, each portable unit will pause for a period equivalent to the product of the acknowledgement message time slot multiplied by count of messages accumulated since the receipt of the particular portable units message.

Abstract: In the preferred embodiment the multiple frequency receiver comprises a decoder responsive to a transmitted coded message signal having a special code for designating that the message is being sent on the local frequency and which is also responsive to the absence of the special code which indicates that the signals are being transmitted on a designated nationwide frequency. The decoder includes a microprocessor which generates an output to turn on the local frequency channel element so that the pager may receive the local frequency when the special code is detected and generates a second output to turn-on a nationwide frequency channel element so that the receiver can receive a nationwide frequency when the special code is absent. This enables the pager user to transfer from his local city to another city without having to manually adjust the pager.

Abstract: A simulcast paging transmitter remote control system capable of individual station control is described. The remote paging transmitter control system comprises an encoder and decoder which interface with a paging terminal and transmitter respectively. The system encoder and decoder communicate through a specifically formatted signalling scheme which is configured to provide station deactivation information as well as conventional paging information.

Abstract: A backlighted liquid crystal display (LCD) assembly has a thin phosphorescent layer positioned between the display and the light source to provide an even distribution of light intensity across the viewing surface of the display. The phosphorescent layer includes a phosphor powder mixed into a resin. The mixture is molded into a thin sheet and then cut to size. The phosphorescent layer and an optional disiccant layer may be encapsulated between sheets of acrylic film. The phosphorescent layer may also include a phosphorescent coating that is applied to the rear surface of the LCD or to the front surface of the light source.