Filter tutorial FR-AM-2 how EMI filters work

A filter works by preferentially selecting certain signal frequencies while absorbing or reflecting undesired signal frequencies; There are many types of signals and filter types and configurations and the filter type and configuration should be selected to match the signal type and the environment that the signal and filter operate within; Actual filter operation will depend on the frequency range the filter operates over and the impact of parasitic component effects over that frequency range; Filter design is straightforward, but there are many subtleties that will determine actual filter performance; Filter design is best handled by someone with significant experience in designing filters, not just someone who had a circuits 101 course; If you are buying a filter from a vendor, makes sure that the performance data you rely on matches your actual source and load impedance.