Comparison of Time Domain Scans and Stepped Frequency Scans in EMI Test Receivers

Taking the R&S ESR EMI test receiver as an example, this paper looks at a CISPR 16-1-1- compliant test instrument with time domain scanning capabilities. The paper compares the measurement speed and level measurement accuracy of a conventional stepped frequency scan versus an advanced FFT-based time domain scan. It also contains guidance on making optimum use of time domain scans.

Table of Contents

1 Motivation ................................................................. 3

2 How an FFT-Based Test Receiver Operates ........... 4

2.1 A Classic Test Receiver ........................................ 4

2.2 A Test Receiver with Digital Signal Processing ..... 4

2.3 The Window Function ............................................ 6

2.4 Overlapping in the Time Domain ........................... 8

2.5 Overlapping in the Frequency Domain .................. 9

2.6 Detectors ...............................................................10

3 Performance Comparison .........................................11

3.1 Comparison of Level Measurement Accuracy .......11

3.1.1 CISPR Band C, Peak Detector ...........................11

3.1.2 CISPR Band C, Quasi-Peak Detector ................13

3.1.3 CISPR Band B, Quasi-Peak Detector..................14

3.2 Comparison of Measurement Speeds ...................16

4 Choosing the Right Measurement Time .................. 17

5 Summary ................................................................. 23