3. Operating Instructions
Figure 3.9.
Smoothed vs. unsmoothed traces at very small vertical scales (
0
.
7
mρ
per
vertical division).
Section 3.11.5). The following TDR trace sample resolution settings are available in the
MENU
→
Resolution
menu option:
1.
Screen
: Screen resolution (1 sample/pixel). Fastest trace, adequate for many routine
cable testing tasks. At large horizontal scales, the resolution is low and small faults may
be undetectable, or at least underestimated. This is because there may be too few samples
in the region of the fault for the fault to be reliably identified on the trace. For example, if
a 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 maximum
resolution is 5.34 ps (less than a millimeter). 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
11
return loss and cable loss traces which may require sampling at resolutions higher than
Normal mode.
Using fine resolution may result in the CT100B buffering. The CT100B will show a green circle
buffering symbol on-screen until buffering is completed.
For larger horizontal scales, the Normal or Fixed sample resolutions provide high resolution
sampling. The trace display 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
only the older 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.
CT100B TDR Cable Analyzers Operator’s Manual
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