Influence of noise on telephone signaling circuit performance

This paper reports results of a comprehensive study of influence of noise on signaling performance of the major a-c telephone signaling systems in use by the Bell System. A problem exists in the evaluation of signaling circuit performance with regard to characterization of both noise and pulsing accuracy. It appears that a good way to characterize noise is to use the 1% (per cent) point on a cumulative level distribution taken with a level distribution recorder with a 10-ms (millisecond) time constant. Pulsing performance can best be characterized by obtaining a distribution of pulse distortion while pulsing over a noise-disturbed circuit. The 2,600-cycle in-band signaling system performs satisfactorily for signal-to-1%-10-ms-noise ratios of about 0 db (decibels). The N carrier out-of-band system is about 6 db better than the 2,600-cycle system. While comparison is difficult due to different circuit action, the 1,600-cycle in-band system is about 10 db more sensitive to noise than the 2,600-cycle system. Some modification of signal-to-guard ratios in the 2,600-cycle system appears to result in performance which is 6 to 8 db better. Tests showed that compandor action is not detrimental to in-band signaling performance.