An apparatus for communicating a signal to or from a downhole tool includes a drill pipe configured to be rotated to drill a borehole, a tubular under axial tension and secured in the drill pipe, and a retention device secured to the tubular and configured to maintain the tubular under the axial tension. The retention device includes a portion extending from a body of the device in a direction that is non-inward-radial with respect to a longitudinal axis of the drill pipe. The apparatus further includes a transmission line disposed in the tubular and in an opening of the retention device and in communication with the downhole tool.
