1982-05-03
1984-04-03
Pellinen, A. D.
179 16AA, 179 18AH, H04M 706
Patent
active
044409796
ABSTRACT:
DC Saturation effects in the VF transformer of a DPT are reduced or eliminated with apparatus diverting cental office battery loop current away from windings of the transformer when a trunk circuit is seized for an off-hook condition of a calling parties telephone handset. A physically smaller transformer having increased inductance may then be employed for providing increased return loss at low frequencies. The apparatus comprises a current amplifier that is electrically connected across tip and ring lines, with a first switch means in its feedback path, and second switch means for AC coupling a transformer winding to the lines. When the trunk is idle for an on-hook condition of the handset, the amplifier is disabled and the lines are terminated with a large resistance. When the trunk is seized for an off-hook condition of the handset, binary PF and CF signals cause the current amplifier to shunt the resistor and to draw a prescribed amount of DC loop current on the lines for energizing a central office A-relay. This also turns on the second switch means for passing VF signals on the lines to and from the transformer, while blocking DC current from the winding, and terminating the lines with a prescribed impedance. When the calling party is dialing, the CF signal opens the feedback path so that the amplifier is turned hard on and off by pulsing of the PF signal for changing the termination impedance and causing resistive pulsing in the central office.
REFERENCES:
patent: 3936614 (1976-02-01), Suntop
McGibbon Gregor D.
Yu Kenneth K.
Cannon Russell A.
Dwyer James L.
GTE Automatic Electric Incorporated
Pellinen A. D.
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