Co-ordination of M1 and N1 telephone carrier systems

The Bell System´s new N1 carrier system is a low-energy cable carrier system and is subject to interference from existing carriers with overlapping frequencies and higher energy levels. This paper is concerned with the development of a suppression device to prevent energy from the M1 open-wire carrier system disturbing the channels of the N1 system. The problem is complicated by the requirement that other types of open-wire carrier systems, notably the 01 system, must work through the suppression unit. Field tests of the suppression unit developed, consisting of a low-pass filter with mid-point grounded indicate satisfactory transverse and longitudinal loss to the unwanted M1 frequencies without degrading the performance of the line at frequencies below the M1 band.