Abstract: In one illustrated embodiment involving a railway communication system, about ten send-receive stations form a transmission section operating at one pair of frequencies in the range above one gigahertz, the stations being arranged at about one kilometer intervals along the route for radio communication with mobile stations moving therealong. A next succeeding similar transmission section operates at a different pair of send and receive frequencies above one gigahertz. All of the stations of a given transmission section may be in communication with a main station by means of a parallel cable connection. A central station then may communicate with mobile stations via the respective main stations. In another embodiment, the stations are implemented as microwave relay stations linked to a main station by the same antenna system used for communication with the mobile stations.

Abstract: All messages broadcast through a two-way radio by a police officer from his vehicle, are recorded on an endless tape loop of a playback recorder. An alerting signal generated by a pretuned oscillator is simultaneously recorded on the tape with each message. Playback operation of the recorder is initiated by a remote radio trigger device so as to replay and transmit the recorded message and altering signal through the vehicle radio for a timed duration.