On the 8752/8753/8720 etc., and pretty much all newer VNAs, even what you call "uncalibrated" is actually calibrated at the factory or at the service center when you send the analyzer for calibration. The problem is that you don't know what cables were used for the factory calibration. Hence, two analyzers that were calibrated with different cables will show different results giving the impression that the hardware is vastly different. I think, the 8510 was the last VNA which showed true uncorrected hardware performance when the instrument wasn't calibrated. And it was impressive!
This factory calibration is in a way similar to the user calibration, but the correction constants are saved in non volatile memory and protected with a jumper on the processor board. This then is the default state of the VNA when it powers up without a user calibration.
A VNA with 35dB return loss is perfectly usable for most work. Realistically, the accuracy improvements for most work are very small as you get past that range. The log scale of the return loss measurement makes it easy to forget that going from 40 to 50 dB return loss requires heroic efforts for an improvement that is tiny in absolute terms.
Vladan
--- In hp_agilent_equipment@..., David Kirkby <david.kirkby@...> wrote:
If you have not calibrated the VNA, then you are just seeing the
uncorrect performance, and the fact that varies is no surprise. In
fact, I'm a bit surprised you managed to get 35 dB uncorrected
......
Dave
