Hi,
I'm developing 21540_52840DK as ble_central. My developing tools are NCS 1.9.1 and VSCODE.
Based on <\NCS\nrf\samples\bluetooth\central_uart > sample, I added USB and address filter to it and set following configs to extend ble payload size.
CONFIG_BT_L2CAP_TX_MTU=251
CONFIG_BT_BUF_ACL_RX_SIZE=251
It works properly but the ble connection seems unusually weak. I use our custom device as peripheral and the connection is quite solid either with phone app or 52840DK(firmware modified from SDK 16.0.1 central_uart), but when connecting to 21540DK, the connection breaks at around 60cm distance.
To exclude the affects of my modification, I tried the original <\NCS\nrf\samples\bluetooth\central_uart > sample, connection strength is the same.
I found this thread but the problem seems caused by 21540 version. I've checked the sticker on my DK and it says v 1.1.0 and 2022.8, so I'm kinda confused...
Then I tried to set FEM TX POWER to 0 since this DK is act as a pure receiver, more specifically:
#FEM21540 CONFIG_MPSL_FEM=y CONFIG_MPSL_FEM_NRF21540_GPIO=y CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=0 CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB_POUTA=0 CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB_POUTB=0 CONFIG_MPSL_FEM_NRF21540_RX_GAIN_DB=13
And the connection to peripheral is strengthened, but no better than 52840DK.
To test the FEM I also flashed in <\NCS\nrf\samples\bluetooth\peripheral_uart > sample, the advertising power was around -26dBm(with 0 distance) and seems like FEM did work comparing to other peripherals. Which part did I do wrong?
Your advice is appreciated,
Thanks,
Ava
