Identifying fault in a custom NRF9161 board

RE: Identifying fault in a custom NRF9161 board

rajeev — Fri, 25 Apr 2025 00:35:40 GMT

Jakub Nagy this is Rajeev, creator of the Conexio Stratus series boards, and I'm happy to hear that our board turned out to be helpful and that you finally managed to fix the antenna path and size issue.

RE: Identifying fault in a custom NRF9161 board

Charlie — Mon, 10 Feb 2025 11:34:57 GMT

Hi Jakub,

Good to hear that you found improvement in the hardware.

I'm not a hardware expert, but I know that some PCB manufacturers offer impedance control. For example, Controlled Impedance PCB Layer Stackup- JLCPCB. You may want to check with your manufacturer to see if they can provide guidance or assistance with this.

I understand your concern. You can start by collecting logs and modem traces from your custom board. The signal strength might give some clues about your antenna performance. You can check this using AT+CESQ. See: Nordic DevZone Discussion for the expected RSRP.

Best regards,
Charlie

RE: Identifying fault in a custom NRF9161 board

Jakub Nagy — Fri, 07 Feb 2025 16:15:10 GMT

Hi Charlie,

thanks for the quick reply.

I did go and re-check the impedance matching on our PCB design. We use a single strip coplanar waveguide with no matching components, the same as the Conexio Stratus Pro board. It turns out that I did in fact use an incorrect trace width. The updated calculation is below along with the trace geometry:

As you can see the impedance should be 8 ohms off the target. Do you think this is significant enough to cause such severe signal loss on this short trace? Waiting for a new board to get manufactured and assembled is a stretch right now.

I might try to measure the impedance with a NanoVNA but with no testpoints it might be difficult. I can also try to cut the trace and connect a coax to the start. Or I can try to put a series cap/inductor to try to compensate. Do you think any of these might work?

Lastly, I can try what you suggested, swapping the SoC between my board and the development board but it might be risky, cause I worry the development board won't work after either.

RE: Identifying fault in a custom NRF9161 board

Charlie — Fri, 07 Feb 2025 10:18:06 GMT

Hi Jakub,

Thanks for reaching out to us regarding this issue. After reading your description, I’d like to share some thoughts.

Since you have the capability to replace chips, have you tried swapping nRF9161 SIPs between your custom board and the Conexio Stratus Pro development board while using the same SIM card?

This kind of cross-testing should help identify the root cause of the issue. I suspect the problem might be related to your custom board, particularly its RF performance. When manufacturing the board with a specific PCB manufacturer, RF tuning may be required, but this is jus suspection.

Additionally, providing logs of your AT commands and a modem trace would be helpful for further analysis.

Best regards,
Charlie