Patent ID: 8670492

Claim:
A data communication system that transmits data by using a power line wiring as a transmission path, the data communication system comprising: a first power line that transmits an AC power source voltage supplied from an external AC power source device; a second power line laid down near the first power line in parallel with the first power line and transmitting the AC power source voltage simultaneously with the first power line; at least one first data communication device connected to the first power line; and at least one second data communication device connected to the second power line, wherein the first data communication device and the second data communication device generate carrier waves having opposite phases to each other by using a reference timing obtained from a waveform of the AC power source voltage, the carrier waves having opposite phases to each other include an in-phase carrier wave having a same phase as an output signal of a carrier wave generating unit and an anti-phase carrier wave having an opposite phase to the phase of the output signal of the carrier wave generating unit, the first data communication device and the second data communication device select any one of the in-phase carrier wave and the anti-phase carrier wave, based on a phase selection setting, and the carrier waves selected are modulated with the data to generate a digital modulating signal.