Influence of Disturbance Current Mode on Correlation Between Radiation Test Sites Using VHF - LISN and CMAD

To improve the correlation of radiated emission measurements between test sites, a very high frequency line impedance stabilization network (VHF -LISN), a coupling/decoupling network for emission measurement of mains (CDNE-M), and a common-mode absorbing device (CMAD) were proposed as the devices that improve inter-site correlation. The result of the international round robin testing (RRT) using two pieces of equipment under test (EUT) has verified an inter-site correlation improvement effect of both EUTs in VHF-LISN and CDNE-M, but the effect varies depending on EUTs in CMAD. As an additional verification of the previous international RRT, we investigated why the effect of VHF-LISN and CMAD was different. Initially, we evaluated the relation between the influence on the common-mode current variation and the impedance value inserted into the protective earth (PE) line by using a CMAD and an artificial EUT. The evaluation result demonstrated that, if the PE line current was reduced by inserting the impedance, the influence due to changes in the termination impedance at the outlet decreases. Based on this result, we evaluated the effects of improvement in inter-site correlation of VHF-LISN and CMAD by changing the PE line current for three piece of EUT. The evaluation result demonstrated that an effect of VHF-LISN did not depended on the PE current, but, in the case of CMAD, almost no effect was gained when the sufficient PE current existed. Because a PE line is directly connected to the frame of EUT in many cases, this result indicates that the device that defines termination impedance at the outlet on the turntable, such as VHF -LISN, is required to improve the inter-site correlation.