Time Domain Reflectometer

Question

How can I analyze the data time domain reflectometer measurement from this picture?

Answer 1

Do you mean you want to interpret what it means? There are several things to see: 1) The initial 48.3 ohm impedance indicates, practically speaking, a fairly low velocity factor (say, velocity is on the order of 0.6c). (In theory we can't know the velocity, except its less than c!). Its probably rated as a 50 ohm line. So you can guess at the distance to the initial mismatch at 4.05e-8s, my guess is about 25-35 feet down the line. 2) The initial hump shows an increase in impedance. Therefore at that distance there is a slightly more open circuit (but not much, and I suspect that's within design specs). 3) The oscillation indicates another change in impedance shortly after. 4) The wavelength varies with signal strength, therefore whatever mismatches the impedance may be non-linear (like active signal receiver(s), for example). However, reflectometers have to do some signal processing to get it right, and that may somewhat distort it.