Maximum TX Power for nrf_dm

[Mark G.]

Hi all,

I am using nrf52833 on a fanstel module BM833 with printed antenna. I am on NCS with Zephyr and my application is based on the nrf_dm example. Currently I can get distance measurements of up to 6meters in open space, which is not as much as expected. 

I tried to increase tx power by setting CONFIG_BT_CTLR_TX_PWR_PLUS_8=y. But it did not see any improvements in the supported range. Which is strange to me. the default is CONFIG_BT_CTLR_TX_PWR_PLUS_0=y, so I would expect a good increase in range. But I did not notice any difference.

What is the proper way to set the maximum TX power? Why do I not see any improvement in range?

Thanks a lot!

My BT configuration:

# BT
CONFIG_BT=y

CONFIG_BT_CENTRAL=y
CONFIG_BT_PERIPHERAL=y

CONFIG_BT_SCAN=y
CONFIG_BT_SCAN_FILTER_ENABLE=y
CONFIG_BT_SCAN_NAME_CNT=1
CONFIG_BT_SCAN_MANUFACTURER_DATA_CNT=1
CONFIG_BT_SCAN_WITH_IDENTITY=y
CONFIG_BT_ID_MAX=1

CONFIG_BT_EXT_ADV=y

CONFIG_BT_DEVICE_NAME="..."
CONFIG_BT_DDFS=y
CONFIG_BT_CTLR=y
CONFIG_BT_CTLR_ADV_DATA_LEN_MAX=192
CONFIG_BT_CTLR_TX_PWR_PLUS_8=y

# Distance Measurement
CONFIG_DM_MODULE=y
CONFIG_MPSL=y
CONFIG_MPSL_TIMESLOT_SESSION_COUNT=1
CONFIG_DM_MODULE_LOG_LEVEL_DBG=n
CONFIG_DM_GPIO_DEBUG=y
CONFIG_NCS_SAMPLES_DEFAULTS=y
CONFIG_DK_LIBRARY=y
CONFIG_DM_HIGH_PRECISION_CALC=y

[Einar Thorsrud]

Hi,

Setting CONFIG_BT_CTLR_TX_PWR_PLUS_8 will set the default Tx power to 8 dBm. I would have epxected a better range than that. How have you placed the module on your PCB? It should be on the edge with the anteanna facing away. Do you have the same module in both ends? And did you adjust the Tx power on both ends?

PS: For distance measurements applications I woudl recommend usign channel sounding which is now part of the Bluetooth spefification. That is only available on the nRF54 series devices, though.