An interface enables an RF signal, a DC power signal, and a data signal to be conveyed between two devices over a single RF cable. In an exemplary application of this invention, a steerable antenna system is coupled to a wireless adapter for use in a wireless network. The steerable antenna includes a plurality of panels that can be selectively activated in response to the data signal, which also determines a direction in which an RF signal is transmitted or received by a selected panel of the antenna. Low pass filters in each device isolate the DC power supply and the load from the other two signals. High pass filters isolate the radio in the wireless adapter and the antenna array from the DC and data signals. The data signal is preferably encoded into a Manchester format that passes through a bandpass filter provided in each device.