Transmitter frequency

[Bob Cherek]

We tested the transmitter and found out that it operates only on 700MHz. Why is that?

The other modems operate on at least four frequencies (800MHz, 1.7Ghz, 1.8Ghz, 1.9Ghz).

This operation of using 700MHz causes problems in connecting to cell towers.

[RM]

Hi Bob,

More details are required to help you further, modem version/SDK, AT commands or prj configs as well as your configurations of the bands.

if you know the bands you would like to operate you can set them to the modem, also frequencies range limitation by the hardware is possible.

Thanks,

Reuven

[SteveLaser]

I am replying on behalf of the original poster.
SDK: 2.4.0
modem versions: we have tried 1.3.4, 1.3.5, 1.3.6

We are using two units to test this problem: our custom board, and a nrf9160 DK.
In addition, and for comparison, we have our old Telit Cat1 modem. In comparison to the Telit, the NRF appears to be extremely bad at making or maintaining connections in non-ideal settings. In our testing lab, the NRF appears to be fine, though in the LTE Link Monitor we usually get 2 bars of signal strength. But we we drive to the edge of town with our NRFs and the Telit, only the Telit works reliably, and it works fine.

Both our custom nrf9160-based boards and the NRF9160 DK have issues connecting, in places where our Telit Cat1 has no problem at all (the sim cards/carrier are the same).
Our spectrum analyzer shows the NRF to only be focused on the ~700mhz, where the telit "searches" other frequencies (as stated by the original poster).

QUESTION: Is it normal for the NRF to operate entirely on the 700mHZ frequency, even when struggling for a connection?

But in all cases, the Telit seems to connect much more easily than the NRF (both the DK and our custom board).

From our testing lab, all modems work fine to connect.
We use extremely basic AT commands in our code (AT+CFUN=1). We were using PSM/edrx, but has removed them for these tests, and we have added no specialty band configurations. %XBCBAND=? shows all bands are supported, and %XBANDLOCK is not active. We have full vanilla settings and have factory reset the modem several times to ensure a basic default configuration.

We have tried external antennas, and the embedded antenna in the DK. There is no difference in behavior.

We have used a basic serial_lte_modem example to ensure a more vanilla prf.conf.

The proj.conf for our main project/custom board, which we have also tested, is:

#
# Copyright (c) 2020 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
#

CONFIG_FLASH=y
CONFIG_FLASH_MAP=y
CONFIG_SPI=y
CONFIG_SPI_NOR=y
CONFIG_SPI_NOR_SFDP_DEVICETREE=y
CONFIG_PM_OVERRIDE_EXTERNAL_DRIVER_CHECK=y

# CONFIG_SPI_NOR_IDLE_IN_DPD=y # this may not be needed as PM is/ power management is enabled. Need to actually test. Stevemark

CONFIG_DEBUG=n
CONFIG_DEBUG_OPTIMIZATIONS=n
CONFIG_DEBUG_THREAD_INFO=n



CONFIG_PM=y
CONFIG_PM_DEVICE=y
CONFIG_DK_LIBRARY=y

CONFIG_UART_1_ASYNC=y
CONFIG_UART_1_NRF_HW_ASYNC=n
CONFIG_NRFX_TIMER2=y
CONFIG_UART_1_NRF_ASYNC_LOW_POWER=n # changed from 'y' during lpuart conversion
CONFIG_NRF_SW_LPUART=n # changed from 'y'

# General config
#CONFIG_LOG_DEFAULT_LEVEL=3
CONFIG_STACK_SENTINEL=y
CONFIG_NEWLIB_LIBC=y
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y
CONFIG_RING_BUFFER=y

# Network
CONFIG_NETWORKING=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_NATIVE=n

# Modem library
CONFIG_NRF_MODEM_LIB=y
# Align the max FD entry to NRF_MODEM_MAX_SOCKET_COUNT(8)
CONFIG_POSIX_MAX_FDS=8
# Enable below for modem trace
CONFIG_NRF_MODEM_LIB_TRACE=n
CONFIG_NRF_MODEM_LIB_TRACE_BACKEND_RTT=n
# Handle modem fault
CONFIG_NRF_MODEM_LIB_ON_FAULT_APPLICATION_SPECIFIC=y

# Use GPIO
CONFIG_GPIO=y
CONFIG_GPIO_NRFX=y

# UART interface
CONFIG_SERIAL=y # STEVEMARK IS IT SAFE TO SET THIS TO =n? 19-Oct-2023
CONFIG_UART_ASYNC_API=y
CONFIG_NRFX_TIMER2=y

# Stacks and heaps
CONFIG_MAIN_STACK_SIZE=4096
CONFIG_HEAP_MEM_POOL_SIZE=32768
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=4096
CONFIG_AT_MONITOR_HEAP_SIZE=4096

# Device power management
CONFIG_PM_DEVICE=y

# FOTA
CONFIG_NRF_CLOUD_FOTA=y
CONFIG_HTTP_PARSER_URL=y
CONFIG_FOTA_DOWNLOAD=y
CONFIG_FOTA_DOWNLOAD_PROGRESS_EVT=y
CONFIG_DFU_TARGET=y
CONFIG_DOWNLOAD_CLIENT=y
CONFIG_DOWNLOAD_CLIENT_STACK_SIZE=4096
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_IMG_MANAGER=y


# FLASH
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_STREAM_FLASH=y
CONFIG_MPU_ALLOW_FLASH_WRITE=y
CONFIG_IMG_ERASE_PROGRESSIVELY=y

# additional adds. Directly and unchagned from NVS example code
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_NVS=y
CONFIG_NVS_LOG_LEVEL_DBG=y
CONFIG_REBOOT=y
CONFIG_MPU_ALLOW_FLASH_WRITE=y

#try this
# CONFIG_SETTINGS_NVS=y

# Settings - these may need to go and may be interfering with NVS
CONFIG_SETTINGS=y
CONFIG_SETTINGS_FCB=y
CONFIG_FCB=y


# nRF Cloud
#CONFIG_NRF_CLOUD_IPV6=y

# BEGIN MASS COMMENTING - the following lines were COMPLETELY REMOVED for 36000 testing. They will likely need to come back!
CONFIG_NRF_CLOUD_MQTT=y
CONFIG_NRF_CLOUD_AGPS=y
CONFIG_NRF_CLOUD_AGPS_FILTERED=n
CONFIG_NRF_CLOUD_PGPS=y
CONFIG_NRF_CLOUD_LOCATION=y
CONFIG_NRF_CLOUD_LOG_LEVEL_INF=y
CONFIG_NRF_CLOUD_GPS_LOG_LEVEL_INF=y
CONFIG_DATE_TIME=y
CONFIG_MODEM_INFO=y
CONFIG_MODEM_INFO_ADD_DATE_TIME=n
CONFIG_AT_MONITOR=y
CONFIG_MODEM_JWT=y
# CONFIG_NRF_CLOUD_CLIENT_ID_SRC_INTERNAL_UUID=n #stevemark, may be needed later
CONFIG_NRF_CLOUD_CLIENT_ID_SRC_IMEI=y            #stevemark, added in place of above
CONFIG_NRF_CLOUD_CLIENT_ID_PREFIX="" # THIS ABSOLUTELY MUST BE HERE. Otherwise all IMEI-based UUIDS will be prefiexed with "nrf-" and ruin everything.


# END MASS COMMENTING
CONFIG_NRF_CLOUD_FOTA_FULL_MODEM_UPDATE=y

#
# SLM-specific configurations
#
CONFIG_SLM_CUSTOMIZED=n
CONFIG_SLM_LOG_LEVEL_INF=y
CONFIG_SLM_EXTERNAL_XTAL=n
CONFIG_SLM_START_SLEEP=n
CONFIG_SLM_DATAMODE_URC=n

# nRF Cloud based location services
CONFIG_SLM_AGPS=n
CONFIG_SLM_PGPS=n
CONFIG_SLM_LOCATION=n

# Steve's Additions
# CONFIG_PINCTRL=y 
CONFIG_SLM_WAKEUP_PIN=1

# Special area to set everything above to N
CONFIG_LOG=y #stevemark
CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_LOG_MODE_MINIMAL=n
# CONFIG_NVS_LOG_LEVEL_DBG=n
# CONFIG_SLM_LOG_LEVEL_INF=n
# CONFIG_NRF_CLOUD_LOG_LEVEL_INF=n
# CONFIG_NRF_CLOUD_GPS_LOG_LEVEL_INF=n
# CONFIG_LOG_MODE_IMMEDIATE=n
# CONFIG_NVS_LOG_LEVEL_DBG=n

CONFIG_LOG_DEFAULT_LEVEL=3
CONFIG_USE_SEGGER_RTT=y # attention here,
CONFIG_RTT_CONSOLE=y
CONFIG_LOG_BACKEND_RTT=y

#CONFIG_LOG_MODE_OVERFLOW=y

#CONFIG_DK_LIBRARY=y

[Charlie]

Hi Stephen and Bob,

Thanks for checking with us about this problem. 

We tested the transmitter and found out that it operates only on 700MHz. Why is that?

According to a previous discussion, I suspect that only band12 is available for your local network operator. With current MFW implementation, modem will prefer the most recent cell/band where it has been in service, and this means it will more likely select that same cell always again after boot. Hence, only ~700MHz(band12) is detected with your spectrum analyzer. If you have a callbox in your testing lab, you can test with setting of other bands.

nrf9160 not able to connect to Bands other than 12 - Nordic Q&A - Nordic DevZone - Nordic DevZone (nordicsemi.com)

SteveLaser said:

Both our custom nrf9160-based boards and the NRF9160 DK have issues connecting, in places where our Telit Cat1 has no problem at all (the sim cards/carrier are the same).

You can not directly compare LTE-M, NB-IoT, LTE-Cat1 so on even with same carrier. There is no guarantee that network operators deploy them in the same cells or area and tune for similar performance.

Best regards,

Charlie

[SteveLaser]

Thank you for your help. I will post here again if we have any follow-up questions.