Measurement Time Considerations for FFT-Based Receivers and Data Reduction for Result Display

Abstract

During the recent years FFT-based measuring receivers for EMI compliance measurements have become a common thing. This is motivated by the outlook to reduce the overall scan time by several orders of magnitude and to get more reliable results by applying longer observation times. An additional benefit are enhanced methods like scan spectrogram and persistence mode to better understand the nature of the observed signal. During the introduction of the FFT-based measuring receiver we learned that an appropriate observation time is the key to comprehensively record the disturbance characteristic of the equipment under test (EUT). Failing to do so will result in erronous measurement results. When it comes to interpretation of the results it is extremely helpful to understand the algorithm which creates from a huge number of single values the graphical representation on the instrument's display.