Results of multifrequency signalling experiments

Describes and analyses trials of signalling systems based on two-out-of-six code, employing different frequencies for the two directions of transmission. Although trials were carried out in Germany, their results are applicable to all European networks. The effects of delay distortion, echo and double echo, line interruptions, clicks and noises, and signalling speed were investigated for pulse and compelled signalling systems. The conclusions are that pulse system is faster because its speed depends only on the delay distortion, but is not suitable if channels are subject to selector noise. The speed of the compelled system is automatically adapted to the channel quality, and the system is unaffected by even substantial noise since it is possible to make special arrangements for signalling to wait until the disturbance is over. A similar protection for a pulse system would necessitate cutting the speed in half.