Medical device manufacturers have recently begun to incorporate wireless communication, such as ZigBee and Bluetooth operating in the unlicensed 2.4 GHz industrial, scientific, and medical (ISM) band, into their medical devices. Wi-Fi, however, is a major source of interference in the ISM band. With patient safety in mind, the FDA has mandated coexistence testing for wireless medical devices [1]. An initial step toward supporting this mandate is to be able to accurately characterize the interfering network in a typical environment. In this paper, a software defined radio (SDR) is employed to serve as a platform for measuring channel duty cycle, packet arrival rate, node distribution, and packet inter-arrival time distribution of 802.11g networks. Theoretical and technical concerns are discussed, and tests performed to assess system integrity are described. Experimental tests examining channel characteristics of an 802.11g network are also reported.