S820E Microwave Site Masterâ„¢ User Guide : Vector Voltmeter : VVM Calibration
VVM Calibration
VVM Calibration versus Save Reference
Which one should be used?
The Save Reference function stores the current measurement and normalizes the main measurement display to the stored value. All subsequent measurements are now displayed as relative to the stored reference value. This function is independent of VVM Calibration and should not be confused with VVM Calibration. The Save Reference function will be used for ALL relative measurements made with the VVM. In comparison, VVM Calibration may not be required for all VVM relative measurements, although it is recommended because it allows for absolute measurement values of the DUTs, including the reference DUT, and it removes any inherent system errors of the instrument itself. VVM Calibration also compensates (via vector error correction) for any test cables, adapters, or fixtures that may have been added between the DUT and the instrument and the appropriate calibration kit.
Absolute VVM Measurements
Absolute, error corrected reflection or transmission measurements may be made on a DUT in VVM mode. For absolute measurements, a VVM calibration is required. The absolute measurement may then be stored as a reference, if required. Vector error corrected measurements on additional DUTs relative to the stored reference can then be made. This provides the best possible accuracy for relative VVM reflection and transmission measurements. VVM calibration removes system errors and defines a known measurement reference plane, which is mandatory for making accurate absolute measurements.
Relative VVM Measurements
Many VVM measurements are made relative to a stored reference, and in these cases, vector error correction may not be required. VVM calibration removes system errors and may improve relative measurement results. For these reasons, when you are making relative measurements, VVM calibration is recommended, but it is not mandatory.
A/B or B/A Ratio Measurements
VVM calibration is not available when making A/B or B/A ratio measurements. In some cases, adding a 3 dB or 6 dB attenuator to each measurement port (A and B) may be helpful to reduce mismatch errors, which cannot be vector error corrected. If attenuators are going to be added, they must be installed BEFORE performing the Save Reference function. Test port cables, adapters, fixtures, or any other items that are needed to connect to the DUT must also be in place before performing the Save Reference function, and must remain in place for the duration of the measurements.
Performing Calibrations
The calibration menu choices are a subset of those found in Calibration, CAA with fewer choices due to the fewer types of measurements that are available with the vector voltmeter.
To view a summary of these settings, begin from the Calibration main menu and press Cal Info. A summary of the Active Cal Settings and the Current Settings of the instrument are displayed (for an example, see Figure: Cal Info Window). Press Esc to close the Cal Info window.
The calibration menu has a Thru Update submenu key (see Figure: Calibration Menu) that allows you to recalibrate the Thru component without repeating the entire calibration sequence. Refer to Thru Update.
For more specific calibration information, refer to Calibration, CAA.