A diagnostic and prescriptive system and method for management of a combined optical and RF cable plant system. In an exemplary embodiment the method and system uses optical receivers in a hub or headend to determine a variety of cable plant parameters such as the OMI of the received signal and automatically facilitated prescriptive service through prioritization and automatic recalibration. In another exemplary embodiment the method allows doing such signal OMI measurements in a closed loop system (that is a fully operational system). In addition, a further exemplary method and system allows storing of standard receiver calibration information such that from thereon signal OMI measurements that can be performed without signal interruption.