Cellular Monitor Trace Captured without Any Packets

[David-AgamControl]

Hello

I have a custom nrf9151 board. I am attempting to capture a cellular traffic trace using the Cellular Monitor app in nRF Connect for Desktop.
In order to do that I have flashed the modem shell sample built with nrf91-modem-trace-uart snippet and changed the UART pins to match my board's setup. I have also flashed the latest modem firmware 2.0.4 and manually selected it instead of automatic selection under "Modem trace database".
I am using a UART to USB bridge. It is the device listed as "CP2102 USB to UART Bridge Controller". If I open up the COM port (In my case COM6) using the serial monitor I can confirm that I am receiving some sort of binary data over UART. When I attempt to start the trace I can confirm that the file size increases, however no packets appear in the monitor or wireshark.
If I stop the trace and attempt to open the file in wireshark using the Cellular Monitor, then wireshark tells me that "No Packets Captured".

What could be the reason for the cellular monitor to not show or detect any packets?

INFO:

NCS version 3.1.1
SDK version 3.1.1
Modem firmware 2.0.4

# nRFConnect System Report - 2026-10-01T12-37-12.047Z

- App: Cellular Monitor
- Version: 2.8.0
- Source: official
- Core version: 5.4.0
- Engine version: >=5.2.0
- System:     Dell Inc. OptiPlex 3060
- BIOS:       Dell Inc. 1.32.0
- CPU:        1 x Intel Core i5-8500 3 GHz 6 cores (6 physical)
- Memory:     18.1 GB free of 31.8 GB total
- Filesystem: C: (NTFS) 236.7 GB 72.8% used

- OS:         Microsoft Windows 11 Pro (10.0.26200) Windows x64

- Versions
    - kernel: 10.0.26200
    - git: 2.53.0.windows.2
    - node: 
    - python: 3.14.4
    - python3: 3.14.4
    - nrfutil nrfutil-device: 2.19.2
- Connected devices:
    - 0001 : COM6
    - 000801016073 : undefined

- Current device:
    - name:          CP2102 USB to UART Bridge Controller
    - serialNumber:  0001
    - cores:         Unknown
    - website:       Unknown

[Syed Maysum Abbas Zaidi]

Hi,

Thanks for reaching out.

Most likely I think this is due to the CP2102 baud rate limitation. As nrf91-modem-trace-uart snippet defaults the trace UART to 1000000 baud (1 Mbaud). But the standard CP2102 tops out at 921600 baud so it physically cannot clock 1 Mbaud. You can try to override the trace UART baud rate in your board's devicetree overlay to a rate the CP2102 reliably supports e.g 921600 but you may still lose some trace packets at high traffic because then it will be below the modem's trace output rate.

The better option would be to use the bridge that supports higher baud rate.

Best Regards,
Syed Maysum

[David-AgamControl]

I have tried lowering the baud rate but that did not work however switching to a different USB to UART bridge that supports up to 3 MBaud rates on spec solved it.