Coaxial cable impedance measurement with AD2 and BNC board

[Matty333]

I am trying to use the analog discovery 2 with the BNC breakout board to measure impedance of coaxial cable terminated with BNC connectors. I am trying to determine if this can tested. I have 75ohm terminations I could use, but I am not aware if the analyzer can be used in this way.

[JColvin]

Hi @Matty333,

I've moved your question to a more appropriate section of the Forum.

This would not be very feasible to do with the Analog Discovery 2/3 with the BNC Adapter, mostly because the Impedance Analyzer instrument within WaveForms relies on using the differential analog inputs of the Analog Discovery device, but BNC cables are single-ended, ultimately resulting in you not having enough analog inputs while using the BNC adapter to correctly set up the needed topology.

You 'could' forgo the BNC adapter and potentially create a setup with the MTE cables; it will be a "little" janky and not getting to use the higher bandwidth of the BNC, but it would work (depending on how accurate of an impedance measurement you are wanting to get from the coaxial cable; impedance measurements work best when your reference resistance is highly accurate and already close to the unknown impedance value).

The Analog Discovery Pro ADP3450, https://digilent.com/reference/test-and-measurement/analog-discovery-pro-3x50/start, does have enough analog inputs to correctly support the topology needed for the Impedance Analyzer (though you might need various t-adapters for the BNC connections presuming I understand your setup), but that costs more than the AD2 already on your desk.

Let me know if you have any questions.

Thanks,
JColvin

[attila]

Hi @Matty333

The impedance of coaxial cable is measured between the core and shield.
The BNC adapter cannot be used directly since this connects shields to common ground.

The impedance analyzer implementation has option for differential measurement but by default and also on the IA Adapter single-ended setup is used.