On the time referencing problem in time domain reflectometry

In dielectric time domain reflectometry (TDR) a crucial point in the evaluation of the Fourier transforms of the incident and reflected pulses is the establishment of a common time origin t 0 . Ideally the TDR system should operate in a self contained way without the requirement of separate instruments or measurements to indirectly define t 0 . The most direct time referencing method is to place a short at the same position as the dielectric-air interface. The common time origin is then obtained by extrapolating the reflected pulse back to the base level. The author makes an estimate of the systematic error of this method, using model calculations.