Voice-band signals are coupled to and from a telephone subscriber line via a low-pass filter which has a shunt capacitor coupled across the line. In order to simultaneously couple above voice-band signals to and from the line, this capacitor is coupled to the line via windings of a transformer. The above...http://www.google.fr/patents/US4456985?utm_source=gb-gplus-shareBrevet US4456985 - Apparatus for coupling signals to or from a two-wire line
Apparatus for coupling signals to or from a two-wire line
