39
Z
Scale
+
Figure 3-17
Figure 3-18
The Cable List in the TDR contains various cable types and their impedances.
The Cable Menu also has an option to enter a cable type, Z
0
and VF manually.
When a specific cable type is selected or entered, it will set the TDR’s Z
0
to that
impedance value. The TDR will keep that Z
0
value centered if the impedance
scale is lowered. See figure 3-19 and note the Cable’s Z
0
is 75 Ohms and the Z
Scale is set to 100 Ohms. This causes the Z Scale to range from 25 to 125
Ohms to keep the 75 Ohm cable centered. For higher Z Scales (200, 500 and
1K Ohms) the cable’s Z0 will be lower in the display.
Figure 3-19