Cables or other metal (antenna-like) structures often couple to sources of common-mode currents and end up radiating, causing product failures during compliance testing. During the troubleshooting process, it would be helpful to determine the resonance of these cables or structures to confirm they are the source of certain harmonic signals.
We could certainly measure the length of the cables or metal structures, but often, they are connected to other conductive assemblies, such as circuit boards or brackets. Because of these system inter-relationships, it’s not always easy to predict the resonances within a system, and so there’s always a little uncertainty as to where to start the troubleshooting process. These simple techniques may help quickly identify potential resonances within your system or product.