Can anyone shed some light on the measurement uncertainty specifications for a HP8753D Network analyser;

Last month our company rented a HP8753D Network analyser complete with HP85032B calibration kit to measure the reflection parameter performance of our product.

When looking at the performance specifications for this analyser (using the specified cal kit with N type connections) the reflection measurement uncertainty is stated as 0.02 for S11 magnitude = 1.

This is copied from the technical specifications manual page 4, and circled in red in the attached file.

This seems be a very large uncertainty, particularly in terms of impedance:

S11=0.999 equates to 100k Ohms

S11=0.979 equates to 4k7 Ohms

This 0.02 S11 magnitude uncertainty equates to a 96% uncertainty in impedance?

In practice of course, both are measured very accurately by this unit.

Have we interpreted these specifications wrongly?

Any help is appreciated.

Thanks in advance,

Josh

Last month our company rented a HP8753D Network analyser complete with HP85032B calibration kit to measure the reflection parameter performance of our product.

When looking at the performance specifications for this analyser (using the specified cal kit with N type connections) the reflection measurement uncertainty is stated as 0.02 for S11 magnitude = 1.

This is copied from the technical specifications manual page 4, and circled in red in the attached file.

This seems be a very large uncertainty, particularly in terms of impedance:

S11=0.999 equates to 100k Ohms

S11=0.979 equates to 4k7 Ohms

This 0.02 S11 magnitude uncertainty equates to a 96% uncertainty in impedance?

In practice of course, both are measured very accurately by this unit.

Have we interpreted these specifications wrongly?

Any help is appreciated.

Thanks in advance,

Josh

So yes, you interpret uncerainty correctly. And you should know that normally the range of impedance for good accuracy is on the order of 5-500 ohms for a VNA. For impedances higher or lower, impedance analyzers should be used.

However, if you are getting good results, it is most likely because the brilliant RF design of the 8753D hardware surpassed all expectations, and continues to do so 15 years later. ;-)