Mohr CT100B Series - A Small Fault in a Long Cable

3. Getting Started
thousand foot cable is displayed on the screen, there is only one measurement about every
two feet.
2. Normal: Sample resolution setting is chosen to match the cable length setting for good
compromise of detail and speed. For SHORT length cable settings, the resolution is 5.34 ps
(less than a millimeter) or better. For MEDIUM length, the maximum resolution is 17.5 ps
(about 2 mm). For LONG length, the maximum resolution is 49.6 ps (about 5 mm). As you
zoom in, the CT100B will adjust resolution.
3. Fixed: Set a sample resolution manually using M-FUNCTION knob; it stays fixed regardless
of screen horizontal scale. Useful for enhancing frequency resolution of S
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return loss and
cable loss traces that may require sampling at resolutions higher than Normal mode.
Using fine resolution may result in the CT100B buffering. The CT100B will show a scanning
progress bar on-screen until buffering is completed.
For larger horizontal scales, the Normal or Fixed sample resolutions provide high-resolution
sampling. The trace displayed on the screen at each pixel is a vertical bar that shows the maximum
and minimum values sampled within the pixel. This feature ensures that any detectable
TDR cable fault is displayed at least 1 pixel wide regardless of horizontal scale.
A Normal sample resolution trace of an 800 ft. (250 m) cable is shown in Figure 3.10. In this case
the high-resolution sampling of the Normal setting ensures that the small fault from a 50 ohm
BNC barrel connector is displayed despite the large horizontal scale. To see this flaw using the
Screen sample resolution mode would require the user to “zoom-in” to show the detail of a short
section of cable, and then to manually scroll the length of the cable using the HORIZONTAL
POSITION knob.
Figure 3.10. A small fault in a long cable. This fault (red circle) in an approximately 800 ft.
(250 m) cable is from a 3 cm barrel connector (0.01% of cable length). The sampling of the
Normal sample resolution setting ensures that the cable fault is displayed at this large
horizontal scale (~50 cm/pixel).
CT100B TDR Cable Analyzers Operator’s Manual 35