Current probes are one of my most-used EMI troubleshooting tools. Frequently, a product’s I/O or power cables are often an appreciable fraction of a wavelength, so are a source of radiated emissions.

Sometimes the best way to describe how to analyze a communication cable common-mode (CM) noise problem is to describe an actual procedure. The following case history, which was provided by the late ...

Spoiler summary: It only takes -60 dB of mode conversion to fail an EMC compliance test if this common signal gets out on unshielded twisted pair cables. If a common mode choke is used, as much as -20 ...