EMC at a Glance

Electromagnetic Compatibility (EMC) is the ability of a device to operate properly in its environment without disrupting the proper operation of other close-by devices. Electromagnetic Interference (EMI) stands for the electromagnetic energy a device emits, and it can cause problems in other close-by devices if too high. Electromagnetic Immunity (EMS) is the tolerance to electromagnetic emissions. You need an EMI receiver to properly measure the EMI a device emits, a Spectrum Analyzer with some specific features that are pre-defined by the CISPR 16-1-1 specification. For this purpose, we use a Rigol DSA815-TG Spectrum Analyzer (9kHz -1.5GHz) with the EMI option. We also use a LISN to isolate the power mains from the device in this test (DUT). You see, the power supplied to the DUT must be clean in order to measure nothing but the noise the DUT delivers, without it including the power line's noise as well. In our lab, we use a TBLC08 LISN that was kindly provided by Tekbox. Finally, to confirm our results, we use a second Spectrum Analyzer, a BB60C with a much wider bandwidth than the Rigol DSA815-TG. The BB60C was kindly provided by Signal Hound, and it can put much more expensive Spectrum Analyzers to shame if used in conjunction with the Spike software.



Every electronics device, including PSUs, can be an EMI source, which, depending on the amount of EMI emitted, can affect the proper operation of close-by devices. EMI can in some extreme cases even render them unusable. In order to minimize EMI noise, some standards have been established. The corresponding standards for IT (Information Technology) products are CISPR 22 and its derivative EN 55022, which is for products sold in the EU. In the EU, every product featuring the "CE" marking has to comply with the EN 55022 standard. Both CISPR 22 and EN 55022 standards divide devices into two classes, A and B. B-class equipment is for domestic environments, so their permitted EMI emissions are significantly lower than for A-class devices.

Although we have acquired two Aaronia antennas, we will only measure conducted emissions since a proper anechoic chamber is a must for radiated emission testing. To identify the EMI source should the need arise, we have at our disposal a set of Tekbox EMC probes (TBPS01) and a TBWA2 wideband amplifier.

EMI Results

As you can glean from the graph above, the EMI filter doesn't do its job well at frequencies below 1 MHz.