A low cost implementation of a passive TDR using an FPGA

This paper presents a method of using TDR (Time Domain Reflectometry) in a passive way to detect and determine the location of irregularities on a transmission line. pTDR (Passive Time Domain Reflectometer) technology [1] was implemented on an FPGA (Field Programmable Gate Array). By using PLL (Phase locked loop) phase shifters and high speed digital counters [2] the system was able to accurately measure the return time of the reflections (created by the irregularities). This enabled the system to accurately determine the location of the irregularities on the transmission line.