Older Anritsu auto calibration units are supported by the MS4640A Series VNAs but with somewhat lower performance and different functionality. Fewer reflection states are available in these older models so an over-determined algorithm is not employed and a different characterization process is typically employed; both of which result in lower accuracy (see data sheets for quantities). These differences are practically less significant at 20 GHz and below where one may use the 36581X; they may be more significant at higher frequencies. The 36582X is an electromechanical switch-based unit unlike the other modules so it may suffer from additional degradation due to switch repeatability.

The characterization load process is similar. It may be required to transfer the characterization file from a floppy to a USB stick for transfer to the VNA (or transfer by network or GPIB).

A maximum of 1601 characterization points are possible on the older platforms so interpolation errors may be higher. These AutoCal units may be re-characterized with the MS4640A Series VNA to increase point count with the caveats discussed in AutoCal Module Characterization.

Autosensing of the AutoCal orientation is not possible. The current orientation must be entered correctly or large errors will result.

Adjustable switch averaging is no longer supported. A factory recommended level will automatically be invoked for electromechanical units.