Patent ID: 7019611

Claim:
A modem coupling circuit for a power line carrier, which is connected to power lines for transmitting and receiving data, the modem coupling circuit comprising: (a) a transformer having a core including a gap formed therein, primary windings constituting a bifilar wound coil which is wound around the core, forming a single layer; and a secondary winding for transmission and a secondary winding for reception which hold the single layer of the primary windings therebetween from above and below; (b) a coupling capacitor connected to a middle point between first ends of the primary windings having a bifilar construction such that the primary windings having a bifilar construction are serially connected to each other with their second ends being connected to the power lines respectively, wherein the secondary winding for transmission is connected to a transmitting circuit, and wherein the secondary winding for reception is connected to a receiving circuit; and (c) current limiting resistances connected to the primary windings having a bifilar construction respectively.