Troubleshooting EMI Like a Pro

This Column discusses a technique for troubleshooting radiated immunity failures in electronic devices using near-field probes. It presents a case study, explains the method's application, and addresses its limitations and safety considerations for bench-level testing.

This article discusses using the reciprocity theorem in EMC troubleshooting, particularly for immunity issues. It describes a case study involving a smart meter and demonstrates how emission measurements can help identify susceptibility problems, highlighting the usefulness of walkie-talkies in testing.

In large systems, such as big cabinets housing numerous electronic components, employing the near-field probe method can be time-consuming and, depending on the voltage level, potentially unsafe (for instance, when dealing with high-voltage circuits requiring isolation). In such scenarios, an alternative approach is necessary.

Solving EMI problems isn’t only about ensuring that a product can meet EMC regulations and standards (although it’s a significant part of the job). Another crucial reason for addressing EMI issues is to enhance product reliability, especially when a product operates in public or industrial areas where there are many different types of noise sources.

Conducted emission tests can provide reasonably accurate results and also serve as a reliable indicator of radiated emissions, as some of these emissions propagate through cable wiring.

During conducted emission tests, one of the challenges manufacturers face is the resonance peaks in the harmonic noise somewhere between 10 MHz and 30 MHz. Often, no amount of filtering will eradicate or attenuate the peak.

In this column, we discuss several important features of a spectrum analyzer not covered in previous articles that are worth your consideration.

Although most modern RF amplifiers have a high voltage device rating against impedance mismatch, special care is needed to prevent impedance mismatch. To avoid impedance mismatch of the power amplifier, often an attenuator is also recommended to be connected between the output of the power amplifier and the flying probe.

An AM radio can be useful for finding both radiated emissions and ESD events. Understanding how radio works is essential for engineers to use this low-cost technology to troubleshoot complex EMI issues.

In this column, the author offers a brief summary of a more systematic approach for using ferrite cores on cables. This summary can serve as a “ferrite core checklist” for design and test engineers.