When measuring signals in electronic circuits some times what you see on the screen is not what you have in the circuit. Parasitic couplings, mismatching, noise pickup, and many other anomalous effects can give you the wrong picture of your problem.
When designing EMI filters how and where the filter is installed is critical to obtain the desired insertion losses. Usually, the effect of a wrong location or installation is not considered in the design of the filter and surprises appear.
EMC radiated problems in HF/VHF ranges are typical in products with switching-mode power supplies (SMPS) as for example flyback and buck converters. Usually no high power is needed to radiate signals well over the legal EMC limits.
Resonances in components are a well-known topic for electronic designers when working in high frequencies (e.g. EMI/EMC). Do not forget to test your components with an impedance analyzer, especially if they are custom magnetic components.
When routing a printed circuit board (PCB), try to avoid critical signals in emissions or immunity close to the edge of the board to create a more robust system for EMI and EMC.
Many of the EMI/EMC problems in electronic products can be avoided or solved with ground (GND) planes. But, be sure your GND plane is a true GND plane.
This month's column explains the concept of near and far fields using simple theory and examples.
S-parameters are very useful to evaluate, understand, and optimize the response of your filters. If you are unfamiliar with this typical tool for RF engineers, this column is for you.
Usually the confidence you have in your measurements is directly proportional to the cost of your instrument. Take care.
A VSWR bridge and a magnetic near field probe (NFP) are very valuable tools to find resonances in RF and EMI/EMC applications as tuning, shielding, etc.