Investigating the Potential of the Low-Cost SDR USRP B200mini as an EMI Receiver

In this article, a compliant radiated emission setup based on a low-cost software-defined radio (SDR) and a transverse electromagnetic cell is presented. The SDR B200mini from Ettus Research is investigated, which incorporates the popular Analog Devices AD9364 transceiver chip. The most demanding requirements for receivers are specified in CISPR band C/D. Therefore, the focus is put on the respective frequency range 30 MHz-1 GHz. For performance verification, test signals specified in the dedicated norm CISPR 16-1-1 are utilized. The results show that the B200mini is capable to measure broadband impulses using the peak detector at an analysis bandwidth of 20 MHz. However, downconversion spurs hinder accurate measurements at low tuning frequencies. To overcome this, a highly linear upconversion stage is presented, offering sufficient dynamic range for quasi-peak detector measurements, which are the benchmark for professional receivers. Owing to the bandpass-filtered output of the stage, the SDR must fulfill less stringent linearity requirements, and downconversion spurs become a minor issue. Combining the SDR with the upconversion stage allows one to use full-scale resolution of the implemented analog-to-digital converters (ADCs) without driving the SDR's analog front end into saturation. By decreasing the bandwidth of the ADC's antialiasing filters to 1 MHz, it becomes possible to fulfill quasi-peak detector requirements. Supplementary to CISPR 16-1-1, the overall system performance is verified by characterizing a test device. It is shown that the results are comparable with accredited electromagnetic compatibility test houses, enabling a reliable estimate of radiated emission spectra.