Eddy current losses in a conductor of a transmission line can be reduced if the conductor can bedivided into twoparallel shells and thecurrent divided evenly between these two. According to the Clogston theory, this may be achieved if the dielectric constant of the space between these two shells is less than that of the lines' main dielectric by the right amount. This paperdescribes the calculation of the properties of a three-conductor Clogston line, its fabrication, the measurement of its attenuation, and additional calculations relating to the termination of the line.The