Abstract: An amplifier for a radio communications system in a shielded tunnel is disclosed. In one example, the amplifier comprises a processor configured to execute a plurality of modules comprising a gain control module and an attenuation control module. Methods and systems are further provided for controlling and monitoring amplifier characteristics.

Abstract: An amplifier for a radio communications system in a shielded tunnel is disclosed. In one example, the amplifier comprises a processor configured to execute a plurality of modules comprising a gain control module and an attenuation control module. Methods and systems are further provided for controlling and monitoring amplifier characteristics.

Abstract: An antenna system for a multi-channel, two-way UHF underground communication includes a base radio station; a non-radiating coaxial cable attached to the transmit/receive connector on said base radio station; radiators affixed to said non-radiating coaxial cable at predetermined intervals along the length thereof, wherein said radiator is insulated from the center conductor of said coaxial cable; and bi-directional amplifiers spaced at predetermined intervals along the length of said coaxial cable.

Abstract: A radio communications system is intended for use by trains in a tunnel. This system includes an antenna subsystem which incorporates a radiating coaxial cable disposed along the length of the tunnel and extending beyond the portals thereof, including surface coverage for transition. Plural bi-directional, in-line amplifiers are inserted along the length of the radiating coaxial cable at predetermined intervals for amplifying the RF signals carried by the radiating coaxial cable. A monitoring repeater and a control repeater are provided along with an interface for joining the two repeaters to the radiating coaxial cable. A monitoring subsystem includes an end-of-train device and a head-of-train device.