Signalling system between main and PBX telephone exchanges - uses same generator for audible sounds and secondary signalling (BE240177)

摘要

The signalling system, for signalling between a main telephone exchange and a PBX has the secondary signalling signals that follow the main signalling signals produced in a simple manner. 50 Hz AC is used for main signalling and AF multiple-freq. signals are used to perform the secondary signalling functions. The AF signals used for making audible sound are also used for secondary signalling signals -- i.e. both audible and secondary signalling signals are derived from the same AF generator. This reduces the number of components. The number of available secondary signals can be increased by combining several one after another.