Effect of shielding, grounding, EMI filters & ferrite beads on radiated & conducted emissions

In this paper measured results are presented to show the effect of shielding slots, seems and cables interconnecting different subsystems on the radiated emissions. It is shown that by using proper shielding Radiated Emission (RE) levels can be reduced by as much as 40dB. Similarly the attenuation of at least 20 dB in measured voltage levels in the conducted emission tests can be achieved by the use of π-filters and chassis ground. In case of power unit, it has also been diagnosed that major cause of conducted emissions (CE) is the switching of DC-DC convertor. Measurements with ferrite beads showed that these are useful only at frequencies below few megahertz.