+31 40 369 01 52
This email address is being protected from spambots. You need JavaScript enabled to view it.
Share on LinkedIn Facebook Twitter Print

Time Domain Reflectometry (TDR) and Time Gating

Time Domain Reflectometry (TDR) is a technique that measures and displays the impedance of a network (cable, filter etc) over time. Traditionally this is done with a device that generates very fast pulses and injects them on the network, and measures the time and amplitude of reflected pulses.

This gives information about the impedance as a function of the time it takes to reflect. And, since the signals travel with (nearly) the speed of light, the time can be translated to a distance through a cable.

We can do the same kind of measurement with a VNA but in a roundabout way. A VNA measures the (reflected) impedance over frequency. We can use a Fourier transform to convert this into a series of impedances over time, just as a TDR instrument produces.

With TDR functions you can analyze a coax cable or circuit impedance as a function of the distance from the measurement port. This gives information about the physical geometry of a network and possible problems.

VNA TDR graphs

One application is Distance to Fault (DTF) analysis, to find the place of a damaged cable.

TDR also makes it possible to apply Time Gating, to filter out part of the Gain response in time.