Build and flash the application with the nrf91-modem-trace-rtt snippet and overlay-modem-trace-shmem.overlay:
west build -p -b <board> --sysbuild -- \
-Dapp_SNIPPET=nrf91-modem-trace-rtt \
-DEXTRA_DTC_OVERLAY_FILE="overlay-modem-trace-shmem.overlay" \
&& west flash --recover
Capture modem traces with Segger J-Link RTT Logger:
JLinkRTTLogger -Device NRF9160_XXAA -If SWD -Speed 50000 -RTTChannel 1 modem_trace.bin
Convert the trace file to PCAPNG with nRF Util or the Cellular Monitor application:
nrfutil trace lte --input-file modem_trace.bin --output-pcapng rtt-trace.pcapng