nRF21540 FEM configuration with ESB protocol

RE: nRF21540 FEM configuration with ESB protocol

ryansmith532 — Tue, 24 Jun 2025 07:17:17 GMT

Thanks for sharing your setup — it's definitely frustrating when expected TX power isn't being reached, especially when range is a critical factor. Have you confirmed whether the nRF21540's MODE and TX_EN GPIOs are being toggled correctly during transmission? Misalignment here can prevent the FEM from entering TX mode properly. poor bunny

RE: nRF21540 FEM configuration with ESB protocol

Kenneth — Mon, 19 May 2025 13:44:21 GMT

Have you tried just building for the nrf21540dk/nrf52840, but update the overlay to fit your gpio pins for the BT840NE?

https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/esb/esb_ptx/README.html#esb-ptx

Then I expect this should work out of the box.

RE: nRF21540 FEM configuration with ESB protocol

Yanis — Fri, 16 May 2025 08:33:22 GMT

I thought that CONFIG_BT_CTLR_TX_PWR_ANTENNA=20 is only for BT protocole not ESB.

I added CONFIG_BT_CTLR_TX_PWR_ANTENNA=20 but could not build (SDK 2.7.0) the code because of the following error :

c:/ncs/toolchains/ce3b5ff664/opt/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd.exe: modules/nrf/subsys/bluetooth/controller/lib..__nrf__subsys__bluetooth__controller.a(hci_driver.c.obj): in function `receive_signal_raise':
C:/ncs/v2.7.0/nrf/subsys/bluetooth/controller/hci_driver.c:296: undefined reference to `mpsl_work_q'
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

I included the following headers :

#include <zephyr/bluetooth/hci.h>
#include <zephyr/bluetooth/hci_vs.h>
#include <zephyr/bluetooth/bluetooth.h>

This is my prj.conf

CONFIG_BT=y
CONFIG_BT_CTLR=y
CONFIG_BT_HCI=y
CONFIG_GPIO=y

CONFIG_MPSL=y
CONFIG_MPSL_FEM=y
CONFIG_MPSL_FEM_ONLY=y
CONFIG_MPSL_FEM_NRF21540_GPIO=y
CONFIG_MPSL_FEM_NRF21540_GPIO_SPI=n
CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=20
CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB_POUTA=20
CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB_POUTB=10

CONFIG_BT_CTLR_TX_PWR_ANTENNA=27
CONFIG_MPSL_FEM_NRF21540_RUNTIME_PA_GAIN_CONTROL=n

RE: nRF21540 FEM configuration with ESB protocol

Kenneth — Thu, 15 May 2025 11:22:01 GMT

Hi,

I get the impression you are not using the MPSL FEM driver, which should take of this. Also, it will by default use 0dBm if you don't set CONFIG_BT_CTLR_TX_PWR_ANTENNA=20.

If you want to control this manually, I guess you need to set TX mode by set TX pin high and RX pin low.

Kenneth

RE: nRF21540 FEM configuration with ESB protocol

Yanis — Wed, 14 May 2025 16:15:14 GMT

Hello,

Sorry for the late response, I took time to further investigate.

First of all, I am using SDK 2.7.0.

We are using an external antenna with a ufl connexion cable, so the placement of the module is not that important.

We've tested in radiated using a nRF52840 DK which measures the RSSI of the signal sent by the FEM nRF21540.

I also measured the current consumption of the nRF21540 using the ppk2.

It seems that when I set :

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10

The RSSI is -26dBm and the current is 65 mA

and when I set :

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=20

The RSSI is -32 dBm and the current is 60 mA

The gain at 10 seems to give better performance and more consumption compared to the gain at 20. It is a little confusing.

RE: nRF21540 FEM configuration with ESB protocol

Kenneth — Wed, 07 May 2025 11:36:55 GMT

Hi,

It would help to know what difference you see, e.g. conducted or radiated. Also make sure you have followed the guidelines of the module manufacturer of placement of the module.

Looking at the answer here it should be straight forward:
How to control NRF21540 in ESB

Kenneth