Time-Domain Surface Scan Method

The necessity of using dedicated EMI-receivers and compliant spectrum analyzers with CISPR detectors is based on an outdated approach. The levels that people perceive from AM/FM radio reception and analogue modulated television broadcast signals as interference is taken as reference. In the meanwhile new detectors: C_AV and C_RMS have been defined of which the software algorithm is patented which, as such, is delaying the acceptance of these new detectors to be included in IEC CISPR 16-1-1. For most of the EMC related issues, there is little need for such specific detectors as one has to recalculate the nuisance that the total disturbing signal provokes per system bandwidth anyhow. The effect that an RF disturbance might have on a broadcasted RF signal with limited bandwidth will be completely different from e. g. sensor applications where broadband demodulation might occurs. As such, EMC compliant products may still cause nuisance when other detection criteria apply. Time-domain based EMC measurement systems have been developed with just a single RF input [ I]. However, for most of the surface and 3D scanning applications 3 or 4 RF inputs are needed e. g. for measuring the 3 orthogonal EIH-field components and the other input is used for synchronisation. For such applications, modern 4-channel digital oscilloscopes can be used which have add-on mathematical analysis capabilities for the signals obtained. By taking time-domain data with sufficient sampling resolution, the influence onto other susceptible systems can be post-calculated by applying the complex response characteristic of the system being interfered. However efficient data reduction is a prerequisite to limit data storage and enable post-processing.