Enhance the test reproducibility of radiated emission by defined cable termination

In this paper, we compared the measured radiated emission levels by real samples according to CISPR 22 at different laboratories. We observed the maximum test difference is 11.9dB over laboratories, which is much higher than claimed measurement instrument uncertainty. We studied various test conditions and concluded that the mains impedance of laboratory is the key factor to measured emission levels. The mechanism for the impedance to affect the radiated emission was explained. By using an impedance adapter to provide defined impedance for the cable termination, the test reproducibility was improved. The maximum test difference is reduced from 11.9dB to 6.4dB over laboratories.