RF impedance of Nordic on dev kit


NRF52 DK has an RF switch which can be used for looking into the Nordic and observe the impedance using a VNA. I observed the same impedance in RX, TX and power off so I used power off for these experiments.

Using my VNA it looks like the impedance is 10 + 8j. Which is very similar to a 50ohm source impedance followed by 1pF shunt C and 4nH series L... Is the impedance looking in to Nordic supposed to be 50ohms or 10+8j?

Maybe I have a calibration issue with my VNA. I have to calibrate-out the VNA-to-switch cable and the RF switch, both Murata (MM8130-2600RA2 and MXHS83QE3000) so we built a custom calibration board (open/short/50ohm). But now there is a real issue setting up this "custom calibration kit" on my VNA, I don't know what parameters to plug in for offset delay and offset loss. I tried setting them to negligable values but Nordic still doesn't look like 50ohms.

Can you recommend a calibration flow? What is the Nordic impedance? Do calibration kits exist for these Murata switches?

Thanks so much!

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  • Hi,


    Something is not right here, this should be much closer to 50 ohm. Not perfect, but close.


    I have no idea if there exist any cal kits for this connector, but I doubt it. What you could do is calibrate using a coax cal kit which you probably have, and adjust the offset by looking at the impedance, increase it until the impedance is 'open'.

    What are you trying to do? I might be able to suggest a better way forward if I knew.


    Best regards,