3. Operating Instructions
1. Create an S
11
return loss plot using the procedure as described on page 49.
2. Select the
S
11
Options
menu, then
Phase Corr. Off
menu option to toggle to
Phase Corr.
On
. The S
11
trace will update, although it might not look visually different, depending on
the settings.
Phase Correction typically works best when started at the S
11
trace test plane. To choose a
different starting point:
3 Use the
SELECT
button to select a TDR trace, position the active cursor where desired,
then press
Phase Corr. Start
. The Phase Correction starting point will go to the active
cursor position, and the S
11
trace will update, although it might not look visually
different, depending on the settings.
3.11.18.4. Time-Domain Gating, or Return Loss (S
11
) Between Cursors
The CT100B is able to use time-domain gating (also called time windowing) to de-embed
features in the time-domain trace for analysis in the frequency domain using the
S
11
Between
Cursors
feature. All other time-domain features are excluded from the analysis so that only the
feature of interest is analyzed. To perform
Between Cursors
return loss, use the following
procedure:
1. Create an S
11
return loss plot using the procedure as described on page 49.
2. Use the
SELECT
button to select a TDR trace.
3. Position the cursors around the feature of interest (e.g., a fault or connector).
4. Select the
S
11
Options
menu, then
Between Cursors Off
menu option to toggle the
S
11
Between Cursors
feature on. The S
11
trace may change to reflect just the features in the
highlighted time-domain cursor interval.
5. Pressing the
Between Cursors On
menu option again will change it to
Between Cursors
Hold
, which will keep the time-domain region fixed while moving the time-domain cursors.
Otherwise, you may select the S
11
trace to make frequency-domain measurements using
the cursors without changing the time-domain windowing.
See Figure 3.34 through Figure 3.36 for an example of an S
11
return loss plot between cursors.
The cursors bracket an SMA barrel adapter between two 3 ft. segments of coaxial cable. The
S
11
return loss plot shows average 34.46 dB loss across the connector. A loosened connector
shows average loss of 26.7 dB across the connector, compatible with 7.7 dB excess return loss
compared with the tightened connector.
3.11.18.5. Return Loss (S
11
) Calibration Standards
Many precision Open, Short, and Load standards have unique offset and coefficient values
included with them. By correcting the S
11
trace with these values, the error introduced by these
terminators can be reduced. To apply or change these standards, do the following:
1. Create an S
11
return loss plot using the procedure as described on page 49.
2. Select the
S
11
Options
menu, then
Calibration Standards
.
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.
52
CT100B TDR Cable Analyzers Operator’s Manual
