Time Domain Reflectometry (TDR) Length Calculator

Enter the velocity factor of transmission line and the round trip time of the pulse to get the distance of the reflection i.e TDR Length. This is usually the distance to the fault in a cable.


  • TDR Length (meters)

What is Time Domain Reflectometry (TDR) Length?

In a cable, transmission line, or any other electrical path, the fault may occur at any instance due to various reasons. This fault or interruption can be determined by TDR. The distance between the source of the cable and the fault is the TDR length. The TDR instrument sends a pulse through the medium and compares the reflections from the unknown transmission environment to those produced by a standard impedance. It sends a low voltage signal and if there is any impedance change within the cable, a reflection will be seen. The TDR measures the time between the release of the pulse and its return from any reflections. By measuring the time and knowing the propagation velocity of the pulse, the distance to the reflection can be calculated. 

How is Time Domain Reflectometry (TDR) Length calculated?

The Time domain reflectometry (TDR) length is calculated by using the following formula.


TDR length = Time domain reflectometry length in m

c = Velocity of light i.e 2.9979 x108 m/s

υ = Velocity factor of transmission line

Td = Round trip time (RTT) between onset pulse and first reflection (in µs)


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