Abstract: A radio frequency (RF) coupler transfers RF power between a first circuit on a rotary shaft and a second circuit relative to which the shaft can rotate. The coupler comprises a first RF transmission line arranged to rotate with the rotary shaft about the rotation axis of the rotary shaft for connection to the first circuit and a second RF transmission line relative to which the first RF transmission line can rotate for connection to the second circuit. The first and second RF transmission lines comprise first and second electrically conductive tracks arranged coaxially around the rotation axis in mutually overlapping relationship to provide RF coupling between the first and second RF transmission lines. Each track has a gap defining a pair of ports. One of the ports of each track is connectable to a respective circuit and another port in the track is connected to a RF reflecting termination. A notch filter tunable to a desired frequency within a predetermined RF band is also described.

Abstract: A spot welding machine having a pair of electrodes connected to the transformer by a pair of closely mounted shunts spaced less than one quarter of an inch to reduce both the current loss and the reactive forces.