The radiated emission due to the in-house broadband power-line communications (PLC) is caused by the common-mode (CM) currents on the power-line network. There are two origins of the CM currents; The one is caused by the unbalance of the PLC modem itself and injected from the modem to the outlet. The other is converted from the DM signal current at the unbalanced elements on the power-line network. Japanese PLC regulation ristricts the CM current measured using the impedance stabilization network (ISN) with the DM impedance of 100ohm, CM impedance of 25ohm, and the longitudinal conversion loss (LCL) of 16dB, which is determined from the LCL measured at the outlets and intended to emulate the in-house power-linen network. However, the PLC modems which are type-approved under the regulation and avaiable in the market cause the radiated emission more than 20dB larger than intended. The direct cause of the excessive emission is the excessive DM signal of the PLC modems. Why the CM current measurement using the ISN allows the excessive DM signal is clarified.
