How does the FEM function need to be activated when running the "peripheral_hr" example under "nRF5340-DK+nRF21540-EK" board under NCS24.0?

[liangzh]

I attempted to run the "peeral_hr" example under NCS2.4.0 and used nRF21540-EK to enhance the signal, but in reality, there was no significant change.

I attempted the following modifications:

1. Add "- DSHIELD: STRING=" nrf215440_ek ""

2. Overlay adds the following code

&radio {
    fem = <&nrf_radio_fem>;
};

But the broadcast found on the phone is only -90dbm, and the effect is the same when nRF21540 is not activated.

What else do I need to modify?

[Kenneth]

Hello,

How have you connected the shield to the DK? For instance you will to connect external antenna to the shield, and you need a coax cable between the DK and shield (e.g coax cable from Murata such as MXHS83QE3000 or MXHT83QE3000).

Kenneth

[liangzh]

Hello,

I connected  the shield to the DK as shown in the figure.

Is there a problem with this?

Kevin Liang

[Kenneth]

Hi Kevin,

If you build with and without -DSHIELD=nrf21540ek you can compare the \build\zephyr\.config file to see the difference between the two build, typically you will see the following have changed:

As you can see, there is no change in output power by selecting the FEM, so to change the output power you need to modify/add to prj.conf:

Description of the kconfig option to set output power:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/kconfig/index.html#CONFIG_BT_CTLR_TX_PWR_ANTENNA 

Kenneth

[gcb]

Could you please provide a reference or link to purchase that cable? It seems to have an SMA Male connector instead of a Female one like this cable, which would allow me to skip using an SMA Male-to-Male adapter between the cable and the shield.

[Kenneth]

Hi, from my understanding the cable you see on the picture is not a standard cable, it's custom made. But looking for instance on digikey I can find for instance both female and male SMA connectors are possible:
https://www.digikey.no/en/products/base-product/murata-electronics/490/MXHS83/180808 

Kenneth