Construction Coordinator Practice Exam

What causes echoes on a waveform TDR?

1. Signal interference from nearby cables

2. The extra distance the TDR pulse travels after initial reflection

3. A fault in the TDR itself

4. Signal distortion from voltage fluctuations

The correct answer is: The extra distance the TDR pulse travels after initial reflection

The phenomenon of echoes on a waveform Time Domain Reflectometer (TDR) is primarily caused by the extra distance the TDR pulse travels after an initial reflection. When a TDR sends out a pulse, it travels down the cable and reflects back when it encounters a change in impedance, such as a fault or a connector. If there are multiple reflections, or if the cable has variations in its characteristics, the TDR may detect these reflections as echoes. The pulse can reflect multiple times off different points in the cable, traveling extra distances before returning to the TDR, which results in additional signals being displayed on the waveform. This behavior highlights the physical properties of the transmission medium and emphasizes how the TDR interprets the time delay of these signals to compute their distance from the measurement point. Understanding that echoes are essentially reflections caused by pulses traveling longer distances after encountering impedance changes aids in diagnosing issues and analyzing the integrity of the cable system. This makes option B the correct choice in identifying the cause of echoes on a TDR waveform.