Nowadays, power line communications (PLC) are a widely used technology in distribution grids, both for automatic meter reading and automation applications. PLC performances (in terms of capacity, coverage, robustness, and data transmission rate) can be significantly affected by electrical network topologies, connected loads and disturbances. Thus, utilities and modem manufacturers are increasing their interest in electrical network characterization. In this framework, a software tool is proposed in this paper to measure received signal and noise levels. As case study, it is implemented on a G3 PLC transceiver, widely used for smart metering purposes. In this way, a PLC channel characterization can be performed without connecting external instruments, by using already installed smart meters with the updated firmware. The software tool allows having a better understanding of signal attenuation influence on communication channel performances. Moreover, possible solutions could be suggested avoiding some frequency bands or regulating some transmission/reception parameters.