Problems in detecting maximum values of interference using VCCI test method - uncertainty in measuring interference pattern resulting from reflection on a metallic ground

摘要

EMI test methods by Recommendation CISPR16, 22 basing on measuring maximum values of electric field intensity in antenna height scanning coping with the possible interference pattern consume a long time for test works, then needs to improve the efficiency of the measurement. Use of the VCCI Simplified Test Method can shorten the time for measurement greatly and produces test results similar to those according to the CISPR recommendations through omitting the antenna height scanning but fixing the receiving antenna height at 4 m for horizontal polarization and at 1 m for vertical polarization. This paper provides discussions to prove that uncertainty found in measurements by the VCCI simplified method may reach even 20 to 40 dB according to analysis of the frequency characteristics of the interference pattern caused by reflection by the metallic ground and that shifting test site from the metallic ground type to the free-space type should be the only way to enhance accuracy of the EMC measurement and improve the test work efficiency.