Thomas,
this is more a question to the designer of VNWA about his implementation (DG8SAQ). Please note that sdr-kits provides a download link (on the small paper of the kit) to a calibration value file for your specific BNC-Cal-Kit. If you load that fle in VNWA, the values will have the correct signs. The screenshot below shows the values for simple SOLT value from my own implementation. Negative numbers! This is also true for the arbritary model. Any reason not to use the arbritary model? This will give you more accurat results. Measuring a capacitor at 430 MHz, this will make a difference. Measuring SWR at 7 MHz, just go ahead with the ideal model.
Regards
Michael, DG5MK
