Evaluation of Methods to Generate Spread Spectrum Time Domain Reflectometry

Reflectometry is used extensively to measure electrical characteristics such as impedance, fault location and detection, and wire degradation due to aging. Reflectometry is often not used on energized systems due to interference, the potential for device damage, or poor SNR. These issues have been solved in wireless communication systems using pseudo-noise (PN) codes. Combining PN codes and reflectometry creates spread spectrum time domain reflectometry (SSTDR). SSTDR enables reflectometry measurements on energized systems. This paper explores the tradeoffs in methods to implement SSTDR systems. Analog circuits can be used for simplicity but come at the cost of size. ASIC design is utilized for smaller circuits with less flexibility and higher initial costs. FPGAs allow for greater flexibility but typically don't go above 600 MHz. Current research is underway to implement SSTDR with software-defined radios (SDR), which will have the advantages of flexibility as well as high frequency options.