In wartime environments, radio frequency interference (RFI) is created by communication devices, jammers, and other electronic sources. The RFI spectrum is assumed to be nonstationary over time, which creates potential to disrupt desired radar operation. The cognitive radar system discussed herein mitigates the effects of RFI by sensing and adapting the transmitted waveform to the widest available (unoccupied) instantaneous bandwidth in real time. Consequently, the radar range resolution and target detection are ameliorated. Results of a prototype cognitive radar implemented on an Ettus X310 software-defined radio are presented.