5. Math Functions
3. Toggle Use Calibration Kit Standards to apply offsets and coefficients to the S
11
trace.
4. Set the Characteristic Impedance in Ohms. This is defaulted to 50.
5. Enter the offsets and coefficient values provided with the Open-Short-Load Calibration
Standards. If none are provided, or they are unknown, set these values to 0.
6. Press OK to change the settings to those set above. The S
11
trace will update, although it
might not look visually different, depending on the settings.
If you do not want to use the values set in the table, toggle Restore Defaults to disregard the values
set in the table and use those loaded from the CT100B internal storage. If this is checked when OK
is pressed, all former values will be overwritten.
5.5.6. Other Return Loss (S
11
) Options
Additional miscellaneous options can be found under SCAN → Math → SParam & Normalize
Tools → S
11
Options → Other S
11
Options, and then toggle the options desired.
• OSL Bases Visible: If not checked, the Open, Short, and Load traces will be hidden after the
S
11
trace is created. This is to help reduce the visual clutter of the display.
• Align Base Traces: If checked, and if the input traces to the S
11
trace all include the internal
cabling, the input traces are aligned to the common first rise of the internal cable.
5.6. Improving S-Parameter Measurements
Note that testing short microwave cables directly from the test port may cause unacceptable noise
due to the presence of secondary reflections in the TDR trace. In general, this shows up as excessive
spectral noise. In this case, time windowing can be used to restore measurement accuracy:
1. Attach a phase stable cable to the test port of the instrument.
2. Place the leftmost cursor just to the left of the end of the phase stable cable.
3. Identify the start of the multiple reflections on the cable under test and exclude this region
with the cursors (see Figure 5.8).
CT100B TDR Cable Analyzers Operator’s Manual 85
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