A case study on the consistency improvement in radiated-emission testing by using LISN

In this paper, a case study on the merit of adding the LISN for radiated-emission (RE) testing is demonstrated. For this study, a site source is created and considered as the device under test. This site source, activated by AC power, can generate harmonic reference signals ranging from 30 MHz to 1 GHz. The site source is then measured for numerous times. A large variation among these measurements is observed. By adding several ferrite cores to the power cord of the site source, the variation can be highly reduced. This implies that the conducted noise onto the power cord may contribute a lot to the uncertainty, since the conducted noise will radiate differently as the impedance of the power system is varied. Therefore, it may conclude that the variation may also be reduced if the LISN is added between the site source and the power system even without using ferrite cores. As the conducted noise along the power cord is unavoidable, the LISN will provide a constant impedance making the noise radiated in the same manner. Based on many detailed measurements, the consistency of the RE testing for the site source is indeed enhanced by adding the LISN.