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It is, therefore, necessary to find out the internal impedances so that optimum filter circuit designs

as well as economical solutions can be implemented.

The internal impedances of the power networks under consideration are usually known from calcu-

lations and extensive measurements, whereas the impedances of interference sources or disturbed

equipment are, in most cases, not or only inadequately known.

For this reason, it is impossible to design the most suitable filter solution without measuring the

equipment characteristics. In this context, we offer all our customers the competent assistance of

our skilled staff, both on-site and in our EMC laboratory in Regensburg (also see chapter on “Ser-

vices offered”, page 32).

3

Selection criteria for EMC components

To comply with currently valid regulations, a frequency range of 150 kHz to 1000 MHz has to be

taken into consideration, in most cases, in order to ensure electromagnetic compatibility; in addition,

however, factors such as low-frequency line interference should be considered.

EMC components must thus have favorable RF characteristics and are ususally required to be ef-

fective over a broad frequency range.

For individual components (inductors) the RF characteristics are specified by stating the impedance

as a function of frequency.

4

Arrangement of EMC components

When designing filter circuits using individual components, observe the following basic rules:

s

The components should be arranged along the lines (see example in fig. 10) to avoid capacitive

and inductive coupling between components and between filter inputs and outputs.

s

As insertion loss of a filter circuit in the MHz range is mainly determined by the capacitors con-

nected to ground, the connecting leads of these capacitors should be as inductance-free as pos-

sible, i.e. short.

s

Filter circuits which are to be installed in devices with limited space must be shielded.

Fig. 10

Correct arrangement of filter components, e.g. on a PC board

General Technical Information