Power Filter Insertion Loss Evaluated in Operational-Type Circuits

Insertion losses of several different manufacturers' 100-ampere power filters were measured in the frequency range 100 Hz to 2 MHz and at a range of power current loads utilizing a newly developed current injection probe. The measurements were made using a technique which, in compliance with IEEE measurement standards, provides a constant voltage source in a filter-in filter-out measurement circuit, where source and load impedance parameters are known. Theoretically derived curves for the power filters installed in circuits with complex source and load impedance are compared to measured curves. Theoretically derived curves for current or voltage attenuation are also compared to insertion loss curves. Significant departures from the MIL-STD-220A specification curves were obtained using this new current injection probe measurement method. Strong saturation effects were found with several of the filters. Wide passband excursions were obtained as predicted by the theoretical treatment. The new measurement technique is described in terms of its relation to IEEE standard definitions of insertion loss. A discussion is given of present and proposed methods in relationship to what is felt is the most useful means of describing a filter's operational characteristics.