I ran a test case simulation as a point of reference to a vna measure. This is 100 feet of RG-213 coax. However, I deliberately made the coax much better and than much worse than typical to compare response differences. You will note the ripples in the return loss plot due to the periodic response of transmission line with a perfect reflection; a short in this case. I compare the S21 insertion loss of the coax with 2x higher loss than with Copper for the center conductor. As expected, the S21 response loss is 1/2 of the return loss due to the double travel of the signal. The two measurement techniques agree quite well. The advantage of course of the short at the end of the line, is no need to drag the coax end all the way back to the vna!
Alan
