Keysight N9923-90001 User’s Guide103Calibration for NA, CAT, and VVM ModesWhy and When to CalibrateThere are well-defined and understood systematic errors that are measuredand calculated during the calibration process. These errors are caused byleakage signals inside the FieldFox, by the frequency response of the FieldFoxreceivers, and by reflections inside the FieldFox that interact with the DUT.After calibration, these errors are removed from subsequent measurements.To maintain highest measurement accuracy, perform a new calibration whenany of the following changes occur:— When any of the following measurement settings change: FrequencyRange, Power Level, IF BW, and Resolution. Therefore, make thesemeasurement settings before calibrating. Increased Averaging, lower IF BW,and higher Resolution all cause slower sweeps and slower calibration times.Learn about Interpolation and Questionable Accuracy in “Interpolation *”on page 119.— When the FieldFox temperature changes more than about 10°F (5°C). Learnmore in “How to monitor the internal FieldFox temperature:” on page 24.— When the connection to the DUT changes, requiring a different jumpercable or adapter.DefinitionsDUT (Device Under Test) The cable, antenna, transmission line, amplifier, oranything else that is connected to the FieldFox that is to be measured.Calibration Standards - OPEN, SHORT, LOAD, and THRU— OPEN, SHORT, and LOAD are ‘reflection’ standards that are used duringcalibration. When an RF signal ‘hits’ these components, the signals arereflected in a predictable manner. These components can also be used toterminate a DUT port during some measurements.—SHORT and OPEN standards both cause 100% of an RF signal to bereflected. The difference between these two standards is whathappens to the phase of the reflected signal, which is beyond thescope of this discussion. Although an OPEN standard is a precisioncomponent, simply leaving nothing connected at the end of a cablecan be a reasonable substitute for an OPEN.—A LOAD standard absorbs almost ALL of the incident signal and verylittle signal is reflected back to the source.
