This document evaluates the performance of an energy detector-based spectrum sensing technique for cognitive radio. The energy detector was implemented using a National Instruments USRP-2930 software defined radio device. Experimental results showed that the energy detector achieved good performance in low signal-to-noise ratio values when detecting OFDM primary user signals. Computer simulations using MATLAB were close to results from the USRP implementation. The energy detector's detection probability increased with higher signal-to-noise ratios and it performed well across all false alarm probability values based on receiver operating characteristic curves.