Mohr CT100B Series - Normalized TDR Traces; Using a Phase Stable Cable to Improve S-Parameter Measurements

5. Math Functions
Figure 5.8. Using a phase stable cable to improve S-parameter measurements on short
microwave cables. Use the phase stable cable (green arrow) and position the rightmost
cursor to the left of the secondary reflections (red circle) occurring after the open or short at
the end of cable under test (blue arrow) so that they are excluded.
4. Perform SParam calibration as described in Section 5.4.
The time-windowed trace will have substantially reduced noise due to exclusion of the secondary
reflections.
5.7. Normalized TDR Traces
This process creates a normalized TDR trace based on a calibrated S
11
return loss trace. A
normalized TDR trace appears as another trace in the region of S
11
calibration. The normalized
trace should be cleaner than the Measured DUT trace, with fewer aberrations. The normalized
trace also has an adjustable rise time to help the operator determine what effect a particular cable
fault will have on signals with differing rise times. The following procedure creates a normalized
TDR trace:
1. Create an S
11
return loss plot using the procedure as described in Section 5.4.
2. From the SParam & Normalize Tools menu, select Apply Normalization.
3. Select Normalize Pulse Rise Time and use the M-FUNCTION knob to select a suitable rise
time for the cable system as applicable. Note that selecting a rise significantly shorter than
the native rise time of the TDR instrument will result in a degraded trace.
4. Note that the S
11
Options, such as the Between Cursors On/Off setting, are used by the
TDR normalization process. If Between Cursors mode is turned on, the normalized trace
information will be taken from the time-windowed S
11
trace.
86 CT100B TDR Cable Analyzers Operator’s Manual