4. Operating Instructions
4.5. Cable Type Library
The CT100B has a library of common cable types and associated velocities of propagation. Vp for
these cable types can be loaded from the library. The user can add custom cable types to the
CT100B as well. The user-added cable types are stored and accessed separately from the standard
cable types.
4.5.1. Load a Cable Type’s Vp
To load a cable type, follow this procedure:
1. Press the FILE button. The File menu appears.
2. Select Reference Cable Types or Custom Cable Types from the menu. An interface appears
that allows you to scroll through the cable types with the M-FUNCTION knob.
3. Highlight the desired cable type and press Select. Vp is now set to the value for that cable
type.
4.5.2. Custom Cable Types
The CT100B is able to save custom cable types. Use the following procedure to save a custom
cable type:
1. Press the FILE button. The File menu appears.
2. Select the Custom Cable Types menu option to access user-editable cable types with menu
options Add New and Select.
3. When Add New is chosen, a window appears for entering a cable type name, a Vp for velocity
of propagation, and an expected characteristic impedance for the cable. When the window
first appears, Vp will be set to the current system Vp, while impedance defaults to 50 ohms.
4.6. Smooth Settings
The CT100B smoothing feature performs temporal averaging to decrease visible noise on the live
TDR trace and improve signal-to-noise ratio (SNR) for first derivative, S
11
return loss, and other
mathematical operations. When you acquire baseline TDR scans of cable assemblies meant for
archiving and future comparison use, it is recommended that at least a moderate level of
smoothing be used so that the vertical resolution of the instrument is used to the fullest extent
possible. The effect of smoothing is most apparent at very small vertical scale settings (that is,
when the trace is zoomed-in vertically). To change TDR trace smoothing:
1. Press the M-FUNC button until Smooth shows up in the upper middle of the screen.
2. Rotate the M-FUNCTION knob until the desired level of trace smoothing is obtained.
A comparison of a smoothed (1,024 trace average) TDR trace to an unsmoothed TDR trace at
0.7 mρ (millirho) per vertical division is shown in Figure 4.8.
CT100B TDR Cable Analyzers Operator’s Manual 45
To Next Page
Loading...