Abstract: A digital data transfer system for transferring baseband digital data between a central location and a patient's room is provided. The system employs the existing coaxial cable network found in hospitals and other institutions. The coaxial cable carries power from a DC power source to the patient's television receiver or other device. Digital data is addressed and transmitted from the central location to the individual patient's room on the coaxial cable by temporarily disconnecting the DC power source from the coaxial cable for each bit which is to be transferred (source switching) and detecting, in the patient's room, the interruption in the flow of DC current through the cable. Digital data is transmitted from the patient's room back to the central location on the same single coaxial cable by temporarily disconnecting the load, e.g.