About Analyzer Calibration
The purpose of analyzer calibration (sometimes called "alignment") is to improve measurement accuracy. Calibration completely characterizes the current measurement hardware; it is not necessary to recalibrate if the or parameters such as range, coupling, channel, span, or frequency band are changed. When the Calibrate Button in the Calibration Dialog () is clicked, the VSA instructs the connected measurement hardware (specified in the Current Analyzer Configuration) to perform a calibration.
Calibrate is only available for hardware configuration that support calibrations. The button is greyed out for those configurations that do not support calibrations.
If a calibration is done when a measurement is paused, the VSA will restart the measurement (rather than continue it) when or the 
button is clicked. Any accumulated average data is discarded. This prevents a measurement from using two different sets of calibration data.
Calibration during instrument warm-up is a good idea, even though full accuracy is not guaranteed until the hardware has warmed up. During warm-up, calibration provides an estimate of the instrument's frequency response that allows some of the measurement algorithms to work more successfully. This is especially true when demodulating some digital formats. Without even a rough calibration, demodulation may fail.
Calibration Status
The software monitors instrument state and indicates current calibration state on the right side of the status line at the bottom of the display. Additionally, the display shows "CAL?" in the Trace Indicator whenever full accuracy is not available (because of incomplete or invalid calibration data, or because corrections are turned off).
Calibration Progress Dialog
A calibration progress dialog is shown if you manually start a calibration or if an auto-cal invoked calibration in VSA takes longer than around 3 seconds. Regardless of whether the calibration progress dialog is displayed, the calibration area in the VSA status bar will always show "Calibrating..." when a calibration is occurring (see Calibration Messages).
The kind of progress indication shown in the calibration progress dialog depends on the analyzer that is connected. Some may show percentage of completion, some may show how many alignments have been completed and the total number of alignments (N of M), and some may show the general progress without an indication of what the units are.
You can cancel a calibration in progress by clicking the dialog's Cancel button. This is a hardware-dependent control that not all analyzer models support.
See Also
