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EMC Box: Measuring radiated emissions in a shielded enclosure and its external cables

This experiment shows a means of measuring leakage of electromagnetic energy through seams of a shielded enclosure to analyse the effects in some test positions around the cover. This cover will be removable and will have 18 threaded fasteners distributed around its periphery.

An oscillator circuit capable of producing a typical periodic clock signal will be put inside the shielded enclosure. The output of the oscillator will be connected to a long twin lead to generate common-mode currents and to investigate their associated radiated emissions.

EMC Box Dresden

Next, to study the emissions, a probe will be placed in each defined test positions to measure the potential difference between the cover and the enclosure. Then, it will be used a ferrite common-mode chokes to suppress the common-mode current. Another solution to reduce the common-mode effects is to connect a filter adapter to the long twin lead. Nevertheless, this two methods will increase the rise/fall time of the signal.

Therefore, the final solution could be to use a gasket to shield the seams of the cover and to achieve emissions reduction as using a ferrite common-mode chokes or a filter adapter, but this method does not increase rise/fall times of the generated clock signal.

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