Abstract: A resonant radiation assembly for RF transmission lines is provided wherein the coupling level between the assembly and the transmission line may be readily adjusted at any point along the longitudinal axis of the line. The outer conductor of a coaxial transmission line is partially milled to provide radiation slots along the line, and the conductor is sheathed in a polyethylene cable jacket. A section of dielectric tubing is longitudinally gapped. Either plural conductive strips in combination with a transversely oriented radiation loop, or a single conductive strip is bonded to the outer surface of the tubing opposite the gap. The tubing is placed over the jacket and translated along the line to the desired operating location. The RF coupling level may be adjusted by rotating the tubing about the transmission line to vary the degree of coincidence between the conductive strip and the radiation slots.