| 摘要 |
PURPOSE:To improve a demodulation S/N at a reception part and to enable high-reliability transmission by compensating a potential change due to the leaked current of a class 3 level ground point in the case of transmitting required data through a cable way by utilizing a ground return current. CONSTITUTION:When detecting a carrier signal voltage impressed to cable ways 1 and 2 at a receiving point, a voltage between the ground side cable way 2 and a class 3 level ground line 4 is detected, and a current flowing to the class 3 level ground line 4 is detected for removing noise, which is contained in this voltage, caused by the output fluctuation of the class 3 level ground line 4. Then, these voltage and current are converted to a prescribed current/ voltage, and a noise voltage is obtained. By subtracting this noise voltage from the voltage between the ground side cable way 2 and the class 3 level ground line 4, a carrier signal voltage removing noise is detected. Namely, a noise component caused by the leaked current contained in the output of a subtracter SUB is suppressed, and the carrier signal voltage reducing the noise component is detected at the output of a filter FT removing a commercial frequency component and impressed to a demodulator DEM.
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