Terminal and Main Station Functions

There are three types of main stations associated with the L5 system. Power feed main stations provide the dc power required by the line repeaters. Switching power feed main stations add the automatic line protection switching equipment for the L5 system. Terminal main stations provide the equipment for multiplex and related functions. This equipment includes the jumbogroup multiplex (JMX), which translates arrays of six analog or digitally derived mastergroup signals to and from line frequency; the L5 line bay, which provides the interface between the L5 line and the terminal equipment, including branching and blocking circuitry; the jumbogroup frequency supply, which provides highly stable signals from which JMX carriers are derived; the basic jumbogroup trunk bay, which processes the JMX baseband signal; and the transmission surveillance system which, in conjunction with the E2 status reporting and control system, allows the remote monitoring and trouble shooting of L5 line and main station equipment. L5 is a hardened system with main stations housed in self-contained, underground buildings. These buildings provide life support and auxiliary power equipment which allow main stations to operate under emergency status for as long as several weeks.