Common- and Differential-Mode Conducted Emissions Measurements using Conventional Receivers versus FFT-Based Receivers

Electromagnetic interference (EMI) instrumentation has significantly evolved over the last thirty years. In this paper, the classical architecture of a conventional receiver is described and compared with the newest architecture of a Fast-Fourier-transform (FFT) based receiver. Additionally, different ways to measure the modal emissions, that is, the common and differential modes, with both types of receivers are described. In a conventional receiver, modal emissions can be measured using an external noise separator. In a dual-port FFT-based receiver, this can be done in the digital domain. Both receivers have been used to measure a device under test emitting non-stationary interference.