Apparatus, systems, and methods may operate to transmit a data signal along a transmission line extending lengthwise along a drill string, the transmission line comprising an outer conductive path provided by a tubular wall of a drill pipe that extends along the drill string; and an internal conductive path extending along an interior passage that is bounded by a radially inner cylindrical surface of the drill pipe and along which drilling fluid is conveyed, the inner conductive path being substantially insulated from the outer conductive path. Additional apparatus, systems, and methods are described.