N9030 calibration with USB

I am using the N9030A with Noise Figure app 1.3.54901.19640.  The instrument has a 3.6GHz internal preamp which is below our DUT range, so a U7227C high frequency USB preamp is connected.

The NF app automatically turns off the internal preamp when USB is connected. OK. With a N4002A SNS, perform a USER noise calibration from 1GHz to 5GHz and save the state in a register.

When the register is recalled, all is well until a frequency change. The red UNCAL alarm appears. This change can be the first operation, i.e. no other setup change. The DUT type is Amplifier, the frequency is within the calibrated span.

My primary usage is remote control, so sending the equivalent frequency command returns this:

    -241,"Hardware missing; Internal preamp not available at all frequency points"

 After several hours I found what seemed to be a workaround, sending this sequence of commands:

    :NFIG:CAL:TYPE INT;

    :NFIG:CAL:TYPE USER;

    :NFIG:CAL:STAT OFF;

    :NFIG:CAL:STAT ON;

Now the valid USER calibration is restored.  Those commands must be separate transactions because the instrument needs an indeterminate time to process some of the steps. Performing that same sequence in local mode also restores a valid calibrated state.

In my larger ATE application the magic workaround failed even after experimenting with re-ordering and delays between commands. I am past my deadline and very frustrated, hoping someone there can explain what to do.

 Scott Bell