Improvement of radiated emission measurement reproducibility by VHF-LISN — Interim results of international inter-laboratory comparison

At present, radiated emission measurement standards do not specify the common mode impedance for the outlet terminal of mains network to equipment under test (EUT) in the test site. Because of the difference in the terminating condition of EUT power cable which dominantly causes radiated emission in the frequency range between 30 MHz and 300 MHz, radiated emission measurements of a tabletop EUT are poor in reproducibility. In an effort to resolve this issue, we developed a device called very high frequency line impedance stabilization network (VHF-LISN) and investigated its effectiveness. After performing the domestic inter-laboratory comparison, we proposed an international inter-laboratory comparison program to CISPR Subcommittee I, and the proposal was accepted. For the comparison purpose, we have investigated the reproducibility also by using a common mode absorbing device (CMAD) and a versatile coupling/decoupling network of AC mains for emission testing (CDNE-M). This investigation is just in progress as a future work of CISPR SC-I WG2 until February, 2014. As a glance from an interim result, we could find that all devices are effective to improve the reproducibility of radiated emission measurement in comparison with the case of no such device. But also we were able to presume that the effectiveness of devices to the measurement reproducibility differs with the type of EUT.