NRF21540 Shield + NRF52833 DK - lower RSSI with shield than without

[lbe]

Good morning everyone,

I need to develop a firmware for a custom board that features an NRF21540 + NRF52833.

I started the development using the official evaluation kits: an NRF52833 DK + the NRF21540 shield.

I started from the example BLE peripheral "nrf_uart", which I compiled for the board nrf52833_nrf52833 and to which I added the -DSHIELD=nrf21540_ek

as indicated in the section "Working with FEM". I used two SMA 2.4GHz antenna with the nrf21540_ek and I used the nrf_connect smartphone app to

record the RSSI of the advertising.

It turned out that if I use the 21540 shield, I got a slightly worse RSSI than if not using the shield (I created a separate build configuration without using the -DSHIELD option).

I have about -55dBm without shield (about 1mt distance) and between -60 and -65dBm with the shield.

Clearly, I put the board and my smartphone in the same conditions and distance.

So, apparently, the 21540 is not used or worst, is badly affecting the signal....

Do you have any clue why this happens? Should I initialize it somewhere in the main.c source code of the uart app to make it work?

I have a fair experience with nrf52 using the old SDK, but I am rather new to the nrf_connect and zephyr environment, so it is possible that I am missing something really basic....

Thanks in advance for your help!

Lorenzo

[JONATHAN LL]

Trying to replicate your results but I am not able to get the same results. 


Testing the "adding an extra antenna to the EK worsens the result" situation but I do not see any change in the that I can prove to be due to the added antenna on the ANT2 port. 

And if you only use RSSI to check the strength of the connection it does seem like it does not improve with the code that has shield enabled. So there I do see the same behavior that you see, only comparing the code with the fix and shield and then unplugging vs plugging in the shield. But using the radio test sample or if I am using the RSSI Viewer app then I do see that signal strength is higher when the shield is connected. So just checking with the phone does not provide the best picture. 

I did test two different versions of the shield, both v1.1.0, but one made in 2021, week 33 and on made in 2022, week 8. They did preform a little different when measuring just RSSI. I have not tested the two version in the lab to see how different they perform as there is often some silicon variation from chip to chip\batch to batch. 

Regards,
Jonathan

[Muhammad Usman]

Hi Jonathan LL  and Lorenzo, 

Thank you for the nice discussion. I have the same working environment and I followed all your instructions as it is. the only difference is that I am using nrf21540 DK.

In the second, case I also have the custom board which is nrf52833+nrf21540. 

I am facing the same issue. Can you please help me in this regard?

Thanks 

Muhammad Usman

[JONATHAN LL]

Hi Muhammad Usman , can you create a new ticket and reference this ticket and if you want you can name me and I will take the ticket. 

You can feed in additional info from the following questions:

Are you getting bad results with the nRF21540 DK? or is that your reference when testing with the nRF52833DK+nRF21540 Shield, and that is what performs bad?

Have you also tested with the RSSI Viewer app from nRF Connect for Desktop?

Are you using the latest version of NCS or version 2.2.0 as Lorenzo or something else?

Regards,
Jonathan

[Muhammad Usman]

Hi JONATHAN LL 

Thank you so much for the response and help! 

Yes, i already created the ticket, please find the link below for the ticket. I will further update this ticket if find more observations.

 nrf21540 working confirmation 

Thanks & Regards,

Muhammad Usman

[JONATHAN LL]

Thanks, will follow up on the other ticket for now.