
Vector Network Analyzer
R&S
®
FPC
178
User Manual 1178.4130.02 ─ 07
6. Select the "Clear Cable Model" menu item at any time if you want to perform mea-
surements without using a specific cable model.
Creating a custom cable model
The R&S
FPC provides two ways to define customized cable models.
The first way is to define a cable model with the "Cable Model Editor" that is part of the
R&S
InstrumentView software package. The R&S
InstrumentView is available for free
on the internet. With this software, you can define a cable model on a PC and then
transfer it to the R&S
FPC. You can then select it just like any other predefined cable
model.
If you do not have access to a PC, but still need a cable model that is not stored on the
R&S
FPC, you can also define the characteristics of a cable temporarily on the
R&S
FPC itself. It is not possible to save these, however. They are lost as soon as you
change them or load another cable model.
1. Press the "Meas" key to open the measurement menu.
2. Select the "DTF Config" menu item to open the DTF configuration.
3. Select the "Define User Model" menu item.
4. Define the cable characteristics with the corresponding menu items.
● "Frequency": Defines the frequency that the cable characteristics apply to.
● "Velocity": Defines the velocity of the cable.
● "Loss": Defines the cable loss at the corresponding frequency.
Note that when you change any cable parameter or load another cable model, the
temporary data is lost and you have to define it again for another measurement.
After you have defined the cable characteristics, you still have to activate the use
of the customized cable.
5. Select the "User Model" menu item to activate the cable characteristics. The menu
item turns light blue to indicate that the cable configuration is active.
18.1.6.2
Cable Length
The R&S
FPC uses the cable length to determine the span for the measurement. The
longer the cable under test, the smaller the span. Together with the cable model, the
cable length is also the basis for the calculation of the cable attenuation. The cable
attenuation in turn is necessary for a correct calculation of the reflection magnitude at
the cable fault. The cable length also defines the scale of the x-axis.
If the cable length you have set is shorter than the actual cable length, the R&S
FPC
does not display the faults of the whole cable. A reflection at the end of the cable will
not be shown. However, deliberately entering a cable length that is too short is a good
way to increase measurement accuracy for a fault that is near to the measurement
plane. If the entered cable length is greater than the actual length, the results for
lengths beyond the actual cable length are obsolete because they are caused by multi-
ple reflections.
Measurements and Result Displays