Comment on ’’Studies in electromagnetic fields and phase constants of a concentric line having a helical inner conductor’’ and ’’An analysis of the wave impedance and the attenuation constants of a concentric line having a helical inner conductor’’

These recent theoretical papers, by the same authors, derive the quantities given in the titles. The authors used a ’’wire’’ model for the helix, which is supposed to be more rigorous than the ’’tape’’ or ’’sheath’’ models used in papers published 25 or more years ago. By using experimental data from a paper referenced by the authors, it is shown that the sheath model fits the measurements better than the wire model used here.