Agilent Technologies 87075C Determining the Best Position for the Calibration Reference Plane

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 3-2for 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 3-2illustrates how to align the reference planes by connecting your calibration standards at the same point that you connect your DUT.

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