Auxiliary Radio Channels for the TH Radio Relay System

The operation and maintenance of the TH and TD-2 radio systems require communication facilities along the route which can be used for the transmission of voice, protection switching and alarm signals. In the TD-2 radio system such facilities are typically provided by wire lines running approximately parallel to the radio route, but often separated by several miles. Where such separations exist, additional wireline facilities are required to connect the individual radio stations with the parallel wire-line route. The desirability of providing narrow-band microwave channels for the transmission of these signals within the frequency allocation of the TH system was recognized early in the TH development. Narrow-band channels which have been designed for this purpose are described in this paper. These channels, called auxiliary channels, serve both the TD-2 and the TH systems where there is a combined installation. Before proceeding with a detailed discussion of the auxiliary channel system, its associated systems and signals will be briefly described. 1.1 The CI Alarm and Control System The CI alarm and control system as it was originally developed for use with the TD-2 system has been described in a paper on that system. 1047