user manual

34 Chapter 3
Test Set Cal and SelfCal
Test Set Cal: An Overview
Other Parameters to Consider
The following parameters, if changed after calibrating, will not invalidate the
calibration, but will cause the “C?” notation to appear at the status bar of the
display:
• Sweep time
• Number of points
•Power level
• IF bandwidth
The “C?” notation indicates that a measurement parameter has changed after a
calibration was performed. For best accuracy, avoid measurements which cause the
“C?” notation to appear.
There is a trade-off between selecting the parameters for best measurement accuracy
and the resulting time required for the SelfCal routine. Generally, as your
parameters are modified for the greatest accuracy, the time required for a SelfCal
increases. For example, selecting a large number of points and a narrow system
bandwidth will improve measurement accuracy but will increase the time needed for
SelfCal. Therefore, when choosing parameters, you will have to weigh the
importance of measurement accuracy versus throughput.
Determining the Best Position for the Calibration
Reference Plane
Most often you will not be connecting your DUT directly to the test set front panel.
More likely, you will be connecting your DUT to a test fixture or test cables that are
connected to the test set. See Figure 3-2 for an example. The calibration reference
plane is where you connect your calibration standards, and the measurement
reference plane is where you connect your DUT. Best measurement results occur
when these reference planes are aligned so that you calibrate out the effects of the
test fixture and its associated cables and hardware. Figure 3-2 illustrates how to
align the reference planes by connecting your calibration standards at the same point
that you connect your DUT.