4. Operating Instructions
Figure 4.11. A horizontally zoomed-in view of the cable fault with active (solid) cursor at
the start of the fault (“toe” region) and inactive (dashed) cursor at the peak of the fault.
The DTF measurement is highlighted (red circle).
4.7.1.1. Ohms-at-Cursor Measurements
The CT100B can display the impedance in ohms (Ω) at the cursor position. A reading before and
after a reflection from a fault shows the impedance mismatch that could cause such a reflection.
Impedance measurements at the first fault in a cable are more accurate than impedance
measurements at more distant faults.
4.7.2. Relative Distance and DTF Measurements
The CT100B displays the absolute distance from cable start and also the relative distance from the
inactive cursor to the active cursor. Note that Vp must be set accurately for the section of cable
between the cursors for the CT100B to measure relative Distance-to-Fault accurately. The pulse
velocity of any part of the cable that is not between the cursors will not affect the relative distance
measurement. To measure the relative distance between two points in a cable, do the following:
1. Move the active cursor to the beginning of the section to be measured.
2. Press the CURSOR button to switch cursors.
3. Move the newly active cursor to the end of the section to be measured.
4. The CT100B displays the distance measured between the two cursors as a “∆” value below
the absolute distance measurement. Figure 4.12 is a 3 ft. segment of 50 ohm cable marked by
small impedance “faults” caused by BNC connectors on both ends.
48 CT100B TDR Cable Analyzers Operator’s Manual
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