Ringing-current and loop-current supply system - uses four current sources simultaneously supplying ringing currents to both legs to reduce harmonics

摘要

The ringing-current and loop current supply system keeps the ringing current esp. low in harmonic content despite relatively large variations in the lengths of subscriber lines. The ringing current contains no d.c. component. All four current sources simultaneously supply their ringing currents to both legs at least during a part of the duration of the ringing pulses. The resulting amplitudes of these superimposed ringing pulses during each part of the duration are smaller than the sum of the magnitudes of the first and second instantaneous amplitudes. No coils, relay contacts, or transformers are used which eases integration.