Time-domain reflectometry from Smith-chart plotting

Attention is drawn to the fact that time-domain reflectometry may be carried out without any special apparatus by measuring the input impedances of a transmission-line system at a number of frequencies, using a slotted line for instance. When these impedances are referred to different planes along the line, and the corresponding plots on the Smith charts are produced, the centroids of these plots yield the reflection coefficient as a function of distance along the transmission line.