Monitoring and level control device for HV line carrier system - uses three pilot frequencies for criteria transmission, and if pilot is missing gives alarm

摘要

The carrier system is used for signal transmission over h.v. power lines and uses a pilot circuit in the transmission and reception directions. Two pilot frequencies are used for derivation of a level control criterion for the receiver i.f. amplifier, and for transmission of a dialling or engaged criterion. When a pilot is missing, a local alarm is given. Pilot frequencies are generated by coherent frequency shifting. At least one further pilot frequency is used for transmission to the opposite station of further criteria for operational states. When these criteria are received, or a pilot is missing, certain functions are carried out.