3. Operating Instructions
2. Select
Vert. Units
to toggle through the different options.
Example trace with impedance (ohms) as the vertical unit is shown in Figure 3.43. Note that
the vertical scale is in ohms and the open fault at the end of the cable on the red (Impedance)
trace shows nonlinear relationship between the reflection coefficient and the impedance
described in Section 5.6.
Figure 3.43.
TDR trace with impedance vertical units (red, top) demonstrating vertical
scale in ohms and emphasis of the open fault at the end of the cable. The black trace
uses reflection coefficient (millirho) as its vertical units.
3.11.23. Layer Peeling (Dynamic Deconvolution) Traces
The CT100B includes the capability to perform layer peeling/dynamic deconvolution. This is a
useful technique for improving impedance accuracy by removing the effects of multiple
reflections caused by impedance discontinuities along the length of the cable. In general, any
impedance discontinuity creates both forward (transmission) and backward (reflection) waves. If
reflected off other impedance discontinuities, these reflected waves will constructively or
destructively interfere along the length of the TDR trace, leading to impedance measurement
errors. The CT100B
Layer Peeling
feature iteratively extracts the underlying reflection
coefficients as described in Section 5.14. For a more detailed description of layer peeling, see
Section 5.14. To create a layer peeling trace, use the following procedure:
1. Position the TDR trace on the screen so that the region of interest is visible with a portion
of 50 ohm cable visible at the left hand of the screen (use the CT100B’s internal 50 ohm
cable if needed).
2. Use the
HORIZONTAL POSITION
knob to place the active cursor on the 50 ohm cable
at the left side of the screen. The location of this cursor will define the start of the left
side of the layer peeling trace.
3. Select
Math
menu.
4. Select
Layer Peeling
menu option.
An example of a layer peeling trace is shown in Figure 3.44. This figure depicts a multi-segment
cable of varying impedance (50-125-75-63 ohms) with an open fault at the end. The corrected
impedance of the final segment is within 2-3 ohms of the actual value, which represents an ~80%
reduction in impedance error when compared with the uncorrected live TDR trace.
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CT100B TDR Cable Analyzers Operator’s Manual
