5. Math Functions
Figure 5.9 shows a normalized TDR trace (blue) with a short fault in a 50 ohm cable. The
normalized trace shows reduced aberrations and more accurate relative reflection coefficient and
impedance after the fault compared with the live TDR trace.
Figure 5.9. Normalized trace (blue, bottom) showing short fault in a 50 ohm cable.
5.8. 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 7.13. For a more detailed description of layer peeling, see Section 7.13. 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 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 5.10. 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.
CT100B TDR Cable Analyzers Operator’s Manual 87
To Next Page
Loading...