Abstract: A communication unit (118) provides service information related to a second communication service to a base site (114) that provides a first communication service to the communication unit (118). The base site (114) receives the service information, stores the service information, and receives a service request for the communication unit (118) to participate in the second communication service. Finally, the base site (114) transmits a control message to the communication unit (118), via a control communication resource, to alert the communication unit (118) as to requested participation in the second communication service.

Abstract: A calling communication unit (210) transmits a dispatch communication request to a communication infrastructure (202). The dispatch communication request includes at least a dispatch identification of a called communication unit (e.g.,216). In response to the dispatch communication request, the communication infrastructure generates an alert message that includes a dispatch identification of the calling communication unit and determines a telephone number associated with the called communication unit. The communication infrastructure then transmits the generated alert message to the called communication unit based on the telephone number associated with the called communication unit.

Abstract: A calling communication unit (210) transmits a dispatch communication request to a communication infrastructure (202). The dispatch communication request includes at least a dispatch identification of a called communication unit (e.g., 216). In response to the dispatch communication request, the calling communication unit receives from the communication infrastructure a telephone number associated with a voice mail server (222) that provides voice mail service to the called communication unit and an identification of a mailbox at the voice mail server. The calling communication unit then transmits to the voice mail server the identification of the mailbox and a voice communication. Finally, the voice mail server stores the voice communication in the mailbox.

Abstract: A simulcast broadcast system wherein two signals (103 and 106) intended for simultaneous broadcast are transmitted from a source site (100) to remote sites (200) discrete from one another. At the remote sites, the two signals are separately processed, including the introduction of appropriate delay (305 and 312), prior to combining them for broadcast in conjunction with other remote sites. One or more monitoring sites (400) can also be provided to monitor reception coherence within the system and to provide operating measurement information to allow automatic control of various simulcast system parameters, including delay.

Abstract: A tunable resonant cavity filter structure is disclosed which includes an enhanced ground return internal to the cavity which effectively eliminates generation of deterioration wide band noise and optimizes unloaded Q as well as rending resonant frequency stable with vibration. In its preferred form, the enhanced ground return is in the form of a ground return clip with reliant radial projections that mate with the threads of the threadable tuning element used to determine final operating frequency. The radial projections are deflected in cantilever fashion so as to generate sufficient pressure to break thru any oxides in the tuning element threads and ensure metal-to-metal contact.

Abstract: A quadrature combiner circuit is provided which employs a quadrature coupler to split an input radio frequency signal into split radio frequency signals which are amplified by respective amplifiers and recombined in a second quadrature coupler in such a manner as to minimize intermodulation distortion products. A feedback loop is employed to assure that the split amplified radio frequency signals incident upon the second quadrature combiner are maintained in quadrature relationship to assure intermodulation product cancellation.

Abstract: An absorptive resonant cavity filter suitable for use on the output of a transmitter power amplifier and capable of substantially constant predetermined resistive input impedance at all frequencies. The structure comprises a bandpass cavity which instead of an input coupling loop employs a conductor coupled from the input and configured along the wall of the cavity to form a transmission line of predetermined impedance and terminated by a resistor of similar impedance value.

Abstract: A variable impedance synthesis circuit is provided for generating a selected impedance, whether real or complex, at a predetermined port. The variable impedance synthesis circuit exhibits the selected impedance in response to control signals applied thereto.

Abstract: Apparatus is provided for inhibiting the generation of intermodulation products in a radio frequency amplifier coupled to a circulator. A control circuit generates a control signal exhibiting indicia of the amount of isolation provided by the circulator. The control signal is provided to a variable impedance synthesis circuit coupled to the circulation isolation port such that the impedance synthesis circuit exhibits the appropriate impedance to maximize circulation isolation. Intermodulation is thus minimized.