The use of electrical and electronic devices is increasing more and more in our world and an end to the growth is not in sight. However, for trouble-free operation of these devices, « electromagnetically compatible » conditions must be present. That is, a device itself must operate satisfactorily in that it does not cause electromagnetic interference in the environment that would be unacceptable to other devices.

Electromagnetic interference can cause various faults that are often not easy to diagnose. These disturbances range from crackling and noise in a radio receiver, to data errors and processor dropouts in computer technology, to insulation breakdowns. In addition, they can propagate in different ways depending on the frequency.

To suppress the conducted interference and to ensure EMC guidelines, mains filters with appropriate values are needed. By maximising the mismatch of impedance, the use of EMC filters prevents the propagation of interference. The filtering effect extends in both directions. This means that interference from the consumer to the mains is attenuated as well as from the mains to the consumer.
Important to know: Low-frequency interferences below 10 MHz mainly propagate line-bound through galvanic couplings. Higher-frequency interference > 30 MHz, on the other hand, is mainly transmitted radiation-bound. The range in between is an addition of transmission mechanisms.