What are the common issues with TDR?

What are the common issues with TDR?

The trigger source is not coerced to Internal Clock when TDR Step generators are manually turned on (see the TDR setup menu).

Tektronix recommends using TDR Preset when setting up TDR. TDR Preset not only sets the trigger source to Internal Clock, it also turns on the TDR step generator and acquisition hardware for the selected channel, and scales and positions the signal so that the incident edge of the TDR pulse is visible on screen. The recommended process follows:

• Connect the channels to be used (the CSA8000 and TDS8000 support TDR on up to eight channels simultaneously) to the Device-Under-Test.
• Press the TDR Preset button in the TDR setup menu for each channel used.
• Following any TDR preset, you can specify step polarity and displayed units for each TDR channel if you want.

Why is the inverted TDR pulse is displayed in a non inverted way?
The volts waveforms will show the inverted step as inverted; the Rho and Ohm are related to impedance, so showing them upside-down (even when the step is inverted) would be incorrect.

See TDR Impedance Measurements: A Foundation for Signal Integrity for more TDR related information.