Abstract: This is a Mode S radio frequency transmission system with coordinated use of a rotating directional antenna and omnidirectional antennas. A software-implemented prefilter both processes messages destined for aircraft equipped with Mode S datalink capable transponders, and prevents any uplink message transmission to a transponder from coinciding with the once-per-scan surveillance interrogation from the rotating antenna as well as any datalink interrogations specified for transmission through the rotating antenna.

Abstract: A programmable key telephone system has a key service unit with a plurality of telephones coupled thereto. The key service unit is controlled by a microcomputer. An alphanumeric display mounted in the key service unit is coupled to the microcomputer and is driven during an installation mode of operation to prompt an installer through a sequence of steps designed to elicit instructions for programming system features. A telephone from the key telephone system is coupled by the installer to the microcomputer and used as a data input terminal to enable the installer to input instructions via the telephone's keys. Non-volatile memory is coupled to the microcomputer for storing system feature data in accordance with instructions entered by the installer. Indicator lamps on the data entry telephone can provide additional prompting or feedback to the installer as to features being programmed. Programming of the system can be accomplished without interrupting normal telephone operation.

Abstract: A key telephone system uses four wires for transmission of voice and audio signals to and from the telephone stations and other components which are part of the system. A plurality of telephone stations are provided, each having a two wire audio input port, a separate two wire audio output port, and a data port. Communcation paths are established through a crosspoint matrix. The matrix includes a first group of addressable crosspoint switches for coupling selected transmit signal paths to selected first link points. A second group of such switches is provided for coupling selected receive signal paths to selected second link points. A third group of such switches couples selected first link points to selected second link points. A link searching routine determines which links are available for effecting communication paths. A minimizing function shares communication paths among common signals when possible.