The Electromagnetic Incompatibility of EMI Filter Test Methods and Test Results

This paper reviews the filter qualification requirements of MIL-F-15733 and the insertion loss test methods and test fixtures of MIL-STD-220A. The inherent measurement errors when testing filters under so called full-load conditions are illustrated. The measurement error is due to the DC isolation networks which give a reactive load instead of a 50-ohm resistive condition. Valid test results can be obtained under the optional no-load conditions of MIL-STD-220A. Revision of MIL-F-15733 is suggested to require insertion loss tests under no-load conditions and to add filter core saturation, capacitor characteristic tests, and limits. A practical approach to prediction and verification of filter effectiveness is suggested.