Unbalanced to balanced signal line coupling device

A coupling device for connection between an unbalanced signal line having a first characteristic impedance and a balanced signal line having a second characteristic impedance, the unbalanced signal line including a grounded conductor, the balanced signal line comprising an unshielded twisted pair of wires, the coupling device comprising:

• a) an input port connectable to the unbalanced signal line and an output port connectable to the balanced signal line;
• b) a balun comprised of a pair of balun input leads, a pair of balun output leads, and a core having a permeability of at least 1,000, the input leads electrically connected to the input port, the balun configured for matching the first characteristic impedance to the second characteristic impedance and for providing a balanced signal at the output leads;
• and
• c) a common mode choke comprised of a core, a pair of windings, a pair of input ends, and a pair of output ends, wherein the pair of windings of the common mode choke are twisted together, each of the windings comprising a conductor portion and an insulation portion, the conductor portions and the insulation portions configured to provide a spacing between the conductor portions such that the twisted pair of windings has a characteristic impedance substantially matching the second characteristic impedance, the input ends of the windings electrically connected to the balun output leads, the output ends electrically connected to the output port.

A coupling device for connection between an unbalanced video transmission cable having a first characteristic impedance and a balanced unshielded pair of wires having a second characteristic impedance, the coupling device comprising:

• a) a mounting board;
• b) a pair of signals lines disposed on the board, the input lines connectable to the unbalanced video transmission cable;
• c) a balun having a core, a first winding, a second winding, a third winding, the three windings connected in series, and a pair of balun output leads, the core having a permeability exceeding 1000, the input signal lines connected across the first winding and the second winding, the output signal lines connected across the second and third windings, the balun having a turns ratio of the first and second windings to the second and third windings such that the balun has an output impedance substantially matching the second characteristic impedance;
• d) a common mode choke comprised of a first core, a second core, and a pair of windings, the first core having a permeability at least 4000 higher than the second core, the pair of windings twisted together, the windings having a pair of input ends and a pair of output ends, each of the windings having a conductor portion and an insulation portion, the conductor portion and the insulation portion configured so that the pair of wires has a characteristic impedance substantially matching the second characteristic impedance, the input ends of the winding electrically connected to the balun output leads;
• e) a pair of output signal lines positioned on the board, the output signal lines connectable to the unshielded pair of wires, the output signal lines connected to the output end of the common mode choke output ends;
• and
• f) a common mode shunt comprised of a core, a first winding, and a second winding, the first winding and the second winding connected at a grounded junction, the first and second windings connected across the output signal lines.