Rain Bird D18600 FD Series 2-Wire Field Decoder (2 address, 2 solenoids) These self-contained switching stations for your central control system are simple, yet very reliable. They work with your central control system just like conventional controllers but are buried underground away from the elements. A simple wiring configuration and absence of protective enclosures keeps installation and maintenance costs low. Rain Bird decoders are a “true lower than 30 volt” system that utilize a two-wire path of 14-gauge wire connecting the central control system, decoders and valves or valve-in-head sprinklers.