FEM Tx Gain Configuration

RE: FEM Tx Gain Configuration

Chandu@1996 — Sat, 15 Feb 2025 02:57:47 GMT

Using only the NRF21540-DK board, I conducted testing by adding FEM configurations in the firmware. I utilized the BLE Mesh Chat example to send 100 bytes of data to the receiver. Following previous suggestions, I measured power consumption using the PPK kit at test points TP26 and TP48. The results showed power consumption exceeding 95mA.

Thanks for the support!

RE: FEM Tx Gain Configuration

Bendik Heiskel — Tue, 11 Feb 2025 10:05:20 GMT

Thanks for the picture, this clears thing up for me. The nRF21540EK is mounted on the nRF21540DK. The nRF21540DK already have a nRF52840+nRF21540 so there is no need to add the nRF21540EK on top of it. The EK is intended to be used with other development kit if you want to use a FEM with for example the nRF5340.

When using the nRF21540DK you don't need to modify the device tree. The board files for the nRF21540DK already have the correct device tree node for the nRF21540, just build for the nrf21540dk/nrf52840 target.

The RSSI viewer app can't really be used for measuring the output power, but you can use it to see if the FEM is actually working, as you will se a higher RSSI when using the nRF21540DK vs a nRF52840DK.

To use the nRF21540EK with a development kit you also need a MXHT83QE3000 cable to connect the RF output of the development kit to the TRX connector on the EK.

RE: FEM Tx Gain Configuration

Chandu@1996 — Tue, 11 Feb 2025 08:12:04 GMT

Hi,
As suggested, by enabling

CONFIG_RADIO_TEST_POWER_CONTROL_AUTOMATIC=y (also reverted the previous changes in proj.conf)

Thereby using total_output_power command to set the total ouput power(aka nRF52840 output power + nRF21540 Tx gain)

Note: Set up env is also added.
And in radio test documentation (https://docs.nordicsemi.com/bundle/ncs-2.9.0/page/nrf/samples/peripheral/radio_test/README.html#testing), it explains about two ways of radio tetesting. Im using RSSI viewer app to test the tx power. But the app has configurable levels only from -110 to -20dbm. How to verify the FEM amplifier with +21dbm settings using RSSI viewer app?

RE: FEM Tx Gain Configuration

Bendik Heiskel — Mon, 10 Feb 2025 14:02:26 GMT

Apologies for the delay.

First of all you should not use 8dBm output power from the nRF52840 with the nRF21540, the maximum tolerated input power on the TRX pin is +5dBm.

[quote user="Chandu@1996"]

I flashed the radio test example on Device A and the RSSI viewer program on Device B.
Device A was set to TX mode using the following commands (as per the README.md instructions):

data_rate ble_2Mbit
start_channel 40
start_tx_modulated_carrier

[/quote]

Based on this screen shot it looks like there is no transmission at all, with 2440MHz being low compared to the rest of the spectrum.

Can you share a picture of your setup?

[quote user="Chandu@1996"]

With FEM (nRF21540-EK)

Changes made in proj.conf:

CONFIG_FEM=y
CONFIG_RADIO_TEST_POWER_CONTROL_AUTOMATIC=n

The radio peripheral output_power was set to 8 dBm.
The FEM module was configured using the tx_power_control command to set FEM_TX_PWR.
However, the total output power still displayed 8 dBm instead of the expected higher value.

[/quote]

parameters_print only show the nRF52840 configuration, since you are building without automatic power control. If you enable automatic power control you can use the total_output_power command to set the total output power, aka nRF52840 output power + nRF21540 Tx gain.

RE: FEM Tx Gain Configuration

Chandu@1996 — Fri, 07 Feb 2025 06:56:23 GMT

Hi,
I checked the test points(TP26,TP48) on the nRF21540-DK alone, after flashing the radio test example with CONFIG_RADIO_TEST_POWER_CONTROL_AUTOMATIC=y enabled. The current measured at these points is around 13-14mA. However, when measuring at the P22 connector (pins 1 and 2), it shows only 0.90mA.

Am I measuring incorrectly?

RE: FEM Tx Gain Configuration

Chandu@1996 — Fri, 07 Feb 2025 05:36:36 GMT

Hi,
Waiting for your reply.
Thanks

RE: FEM Tx Gain Configuration

Chandu@1996 — Thu, 06 Feb 2025 12:51:38 GMT

I tested the radio functionality using two boards:

Device A: nRF21540DK
Device B: nRF52840-DK

Test Setup

Without FEM (nRF21540-EK)

I flashed the radio test example on Device A and the RSSI viewer program on Device B.
Device A was set to TX mode using the following commands (as per the README.md instructions):

data_rate ble_2Mbit
start_channel 40
start_tx_modulated_carrier

With FEM (nRF21540-EK)

Changes made in proj.conf:

CONFIG_FEM=y
CONFIG_RADIO_TEST_POWER_CONTROL_AUTOMATIC=n

The radio peripheral output_power was set to 8 dBm.
The FEM module was configured using the tx_power_control command to set FEM_TX_PWR.
However, the total output power still displayed 8 dBm instead of the expected higher value.

Can you help me troubleshooting, why the FEM module isn't increasing the output power?

RE: FEM Tx Gain Configuration

Bendik Heiskel — Wed, 05 Feb 2025 09:35:44 GMT

The test points are only relevant for the nRF21540-DK, the nRF21540-EK have a separate power measurement connector P5. To use it you need to remove R3, this is shown in the nRF21540-EK documentation:

https://docs.nordicsemi.com/bundle/ug_nrf21540_ek/page/UG/nrf21540_DK/prepare_board.html

RE: FEM Tx Gain Configuration

Chandu@1996 — Wed, 05 Feb 2025 03:26:43 GMT

Hi,
The test points you mentioned are connected to the nRF21540 SOC on the DK board. However, when using the nRF21540-EK, I'm bypassing the SOC on the DK board. Do you think it's still a viable option to check those test points in this setup?

RE: FEM Tx Gain Configuration

PaKa — Mon, 03 Feb 2025 11:32:10 GMT

If you measure current on the nRF21540 DK then the power to the nRF21540 doesn't go through the measurement header: you only measure the current to the nRF52840 (you can see this in the schematic of the DK).

If you use the DK then the output power will be -20/30/40dBm (dont' remember the number from the top of my head but it is very low) if you haven't gotten the nRF21540 enabled correctly. This should be possible to detect by looking at the RSSI on the receiver side.

RE: FEM Tx Gain Configuration

Bendik Heiskel — Mon, 03 Feb 2025 10:32:09 GMT

Hi,

The current measurement connector on the nRF21540DK only measures the current draw of the nRF52840, to measure the current draw of the nRF21540 you need to cut solder bridge SB16 and connect the ammeter between TP26 and TP48:

[quote user=""]

Are there any additional configurations required to ensure the FEM is correctly enabled?
How can I confirm that the FEM is active during TX?

[/quote]

The configuration looks correct, to verify that the FEM is working you can use the RSSI Viewer application in nRF Connect for Desktop. If you test the same application on a nRF52840DK you should see that the measured RSSI is lower than on the nRF21540DK.

Best regards,

Bendik