This is not possible either, however, because leakage currents are severely limited. So, the two best methods of blocking RFI are not available, and designers are forced to rely on less-effective shielding and filtering methods. To eliminate RFI during patient-cable connections, designers must divert as much of the interference currents from the isolated circuit area as possible. With unshielded cables, the only option is to use filters. It is imperative that filters perform properly to ensure success.
Most filters fail to do the job because of poor component selection and poor layout.
At higher frequencies, filter components degrade and coupling factors become increasingly efficient. Therefore, any modeling must account for the parasitic capacitance and inductance within the filter components and between adjacent components and traces. We call this the hidden schematic . If care is not taken to minimize these effects, the filter won't work properly. Unintended filter resonances will occur at distressingly low frequencies, often below 10 MHz, rendering the filter ineffective above resonance.