Figure 1 shows an example of this procedure. Deriving reliable filter attenuation figures from manufacturers' data. When filters are chosen using this technique to try to meet the predicted or actual requirements, their performance can be as good as or better than expected. But any alternative method would require knowledge of the RF impedances at either port, which is not normally available. Layout and Installation Incorrect filter construction or mounting technique can easily compromise radiated emissions and immunity.
Poor shielding can easily compromise conducted emissions and immunity.
The correct way to view filtering and shielding is as a synergy where each task complements the other. Placing it at a distance from the barrier would allow cables between the filter and the barrier to breach this protection. An example of the application of these principles is given in the next section. In addition to this general rule, filters should be located as near as possible to the apparatus that is expected to be the source or victim of disturbances to minimize the impedance of the connection. If the filter needs to be positioned outside the protected area or apparatus, the wiring between the filter and the protected area should be twisted and positioned close to the earthing structure.