MIL-STD-461 Testing and Common Mode Filtering

The present method fo1 making conducted interference measurements as specified by Mil-Std-461A requires sampling of the interference current conducted on power lines between the unit under test and a 10 μF capacitor placed in the line at a distance of 1 meter from the unit. The presence of this capacitor during the test generally restricts unit power line electromagnetic interference filters to those with inductive inputs, since any realizable filter capacitor would be useless in parallel with the 10 μF test capacitor. The usual approach is to use an 'L' type filter with the inductor facing the power source.