What causes an echo in a waveform TDR?

An echo in a waveform Time Domain Reflectometer (TDR) is primarily caused by the extra distance that the TDR pulse travels after reflecting. When a TDR sends out a signal, it travels along the transmission medium until it reaches a junction or a discontinuity, such as a connector, fault, or open circuit. At this point, some of the signal reflects back towards the TDR, resulting in an echo.

The echo is influenced by the overall distance the signal travels, including the distance to the reflection point and back. This means that the longer the wave travels after the reflection, the greater the time taken for the echo to return, which will show up as a distinct reflection on the TDR display. The characterization of the returned waveform allows the construction coordinator to determine the location and nature of the fault or anomaly in the cable.

Other choices pertain to aspects of signal transmission but do not directly cause an echo. The speed of the TDR pulse does not change in a way that would generate echoes; rather, the pulse speed is a constant based on the medium being tested. Signal loss over distance leads to weaker returns but does not inherently create echoes. Interference from external signals may distort or mask the readings but is not a fundamental