One of the important tasks of national regulators is to detect abusive usage of the radio-frequency (RF) spectrum. This talk presents the implementation of an opportunistic spectrum scanner on a software-defined radio platform, whose aim is to continuously scan the RF spectrum and to detect whether any signals are present. The implementation is done on a USRP-N210 software-defined radio, a popular and cheap model. One major bottleneck of USRP-based implementations is the limited CPU computation power, which does not allow to process RF signals at high sample rates continuously. In the proposed implementation, most computation is done on the USRP FPGA, such that the host CPU is relieved and is only used to store data and coordinate the scanning. We present the details of the FPGA and the software architecture, as well as some experimental results that show the efficiency of the proposed spectrum scanner.