The function of an antiparasitic filter is to reduce the disturbance level to an admissible value to comply with the different standards or to reduce the sensitivity of an appliance within a given frequency range. For certain applications (HEMP - Lightning) protection against overvoltage is integrated into or added to the filter.
Antiparasitic filters are of the mismatched “Low-pass” type, except for special applications in telephone networks or in data transmission where they can be matched with impedance values of 50, 75, 100,120 or 600 Ohms in their band pass-range.
These filters operate by impedance mismatch in the frequency in which they are to provide their efficiency called “insertion loss”.
When selecting the structure of a filter, it is necessary to take into account the source and load impedance values, within the frequency range for which the disturbance level is to be reduced.