Insertion loss is quite simply a measure of the effectiveness of an EMI filter. Insertion loss is defined as the ratio of voltages across the load without the filter inserted in the circuit and with the filter inserted in the circuit.
Filter performance is also dependent on the input and output impedance seen by the filter. Insertion loss is therefore measured with 50 ohm source and load impedances as a standard. While this provides a standard for comparison, it does not necessarily reflect the actual performance of the filter within your system.
Since filter performance is specific to the attached system, JMK maintains a test facility to test the individual needs of our customer’s power supply to select or design an appropriate filter. Normally such testing is offered by JMK free of charge.