Communication transformer for power line communication

1. A communication transformer comprising:

a single magnetic core; and

a plurality of conductors which are wound only on said single magnetic core in a spiral shape and are mutually insulated from each other,

wherein said plurality of conductors includes:

a plurality of transfer-purpose conductors for transferring a signal;

an additional conductor which does not transfer said signal and which has a first end and a second end;

wherein a portion of said additional conductor between said first end and said second end is connected to a constant potential,

wherein said portion of the additional conductor corresponds to a portion thereof where an impedance of said additional conductor is subdivided by approximately two, and

wherein both said first end and said second end are floated.

2. A communication transformer as claimed in claim 1 wherein both said transfer-purpose conductor and said additional conductor correspond to electric wires.

3. A communication transformer as claimed in claim 1 wherein said additional conductor is provided between said transfer-purpose conductors.

4. A communication transformer as claimed in claim 3 , wherein said plurality of conductors are comprised of a plurality of additional conductors; and

one of said transfer-purpose conductors is provided between said plurality of additional conductors.

5. A communication transformer as claimed in claim 3 wherein said additional conductor has a sectional area which is larger than a sectional area of said transfer-purpose conductors.

6. A communication transformer as claimed in claim 5 wherein any one of said transfer-purpose conductors which is located adjacent to each other via said additional conductor has a sectional area which is larger than a sectional area of the other of said transfer-purpose conductor.

7. A communication transformer as claimed in claim 1 wherein at least one of said transfer-purpose conductors corresponds to a center conductor of a shielded line; and

said additional conductor corresponds to a shielding conductor which covers an outer circumference of said center conductor.

8. A communication transformer as claimed in claim 1 wherein said transfer-purpose conductors and said additional conductor are provided on said magnetic core in a substantially equi-interval.

9. A communication transformer as claimed in claim 1 further comprising:

inductance elements which are connected to both terminals of at least one of said transfer-purpose conductors.

10. A communication transformer as claimed in claim 9 wherein a transfer frequency range used to transfer said signal is set to be in the vicinity of a series-resonant frequency defined by both a stray capacitance produced between the transfer-purpose conductor to which said inductance element is connected and said additional conductor, and said inductance element.

11. A communication transformer as claimed in claim 10 further comprising:

a capacitance element which connects said portion of said additional conductor to said constant potential; and

said transfer frequency range is set to be in the vicinity of a series-resonant frequency defined by said stray capacitance, said inductance element, and said capacitance element.

12. A communication transformer as claimed in claim 10 wherein said inductance element can be adjusted in such a manner that said series-resonant frequency is set to be in the vicinity of the transfer frequency range.

13. A communication transformer as claimed in claim 9 wherein an inductance of said inductance element corresponds to a leakage inductance of said transfer-purpose conductor.

14. A communication transformer as claimed in claim 9 wherein said inductance element corresponds to a common-mode choke coil.

15. A communication transformer as claimed in claim 2 further comprising:

a capacitance element which connects said portion of said additional conductor to said constant potential.

16. A communication transformer as claimed in claim 1 wherein said portion of said additional conductor is connected to the ground potential.

17. A communication interface module comprising:

a communication transformer comprising: a single magnetic core; and a plurality of conductors which are wound only on said single magnetic core in a spiral shape and are mutually insulated from each other, wherein said plurality of conductors includes: a plurality of transfer-purpose conductors for transferring a signal; and an additional conductor which does not transfer said signal and which has a first end and a second end, wherein a portion of said additional conductor between said first end and said second end is connected to a constant potential, wherein said portion of the additional conductor corresponds to a portion thereof where an impedance of said additional conductor is subdivided by approximately two, and wherein both said first end and said second end are floated;

a transmission-and-reception unit for processing said signal; and

a transfer path connected via said communication transformer to said transmission-and-reception unit, for transferring therethrough said signal.

18. A communication transformer comprising:

a single magnetic core; and

a plurality of conductors which are wound only on said single magnetic core in a spiral shape and are mutually insulated from each other;

wherein said plurality of conductors includes:

a plurality of transfer-purpose conductors for transferring a signal,

an inductance element connected to each of both terminals of at least one of said transfer-purpose conductors and

an additional conductor which does not transfer said signal and which has a first end and a second end, wherein a portion of said additional conductor between said first end and said second end is connected to a constant potential, wherein said portion of the additional conductor corresponds to a portion thereof where an impedance of said additional conductor is subdivided by approximately two, and wherein both said first end and said second end are floated.

19. A communication transformer as claimed in claim 1 wherein said communication transformer is operable to perform power line communication.

20. A communication transformer as claimed in claim 1 wherein said communication transformer is operable to perform communication in a frequency range of 1-100 MHz.