nRF21540 difference between +10 dBm and +20 dBm mode when using with a cellphone

[puz_md]

Hi,

we are using the nRF5340 with the nRF21540 (Fanstel BT40N module). I understand that different regions allow for a maximum of +10 dBm or +20 dBm in transmit power dependng on the region. Further, I understand that the nRF5340 provides a 13 dB gain in Rx power. I also understand that using the FEM on both communication partners will bring the maximum rage gain.

As mentioned above, we have normal cellphones as communication partners. We already could observe that the FEM provides significant improvement in range. Although, my colleagues could not observe significant range differences when switching between +10 dBm and +20 dBm Tx power. Do you have any experience in this respect? Could it be that the transmit power of the cellphone cannot keep up with the +20 dBm Tx power of the FEM, and as Rx power is only increased by 13 dB, packets from the cellphone to the Nordic device will get lost at around the same distance, rendering the +20 dBm Tx power kind of useless?

If there is no way to improve range to a cellphone in the FCC region (+20 dBm) over the ETSI region (+10 dBm), we might drop the +20 dBm support completely as it only adds complexity to the lifecycle of our product... although it would be nice if you know of a way to benefit from the FCC regulation.

Best regards,
Michael

[Kenneth]

Hello,

I am sorry to say, but don't have any experience with this in specific, but what you write do make sense. 

Something you may try is to program the board with the beacon example (since that is transmit only), and check if there is a distance difference with +10dBm vs. +20dBm then (I would expect that).

Kenneth

[puz_md]

Hi Kenneth,

we could see the advertising from a greater distance when using +20 dBm, this should be the same effect as the beacon example you mentioned. Although this does not cover our usecase with bidirectional communication.

Anyway, thanks for the quick feedback!

Best regards,
Michael

[PaKa]

I would check that you have set up the power correctly then to validate that you are actually changing the output power. Are you setting the antenna power in your code? Default for this is 0dBm.

Note: the 13dB gain in the LNA does not mean you get 13dB better link budget. The LNA brings the sensitivity up to around -100dBm. This is as the Noise Factor of the LNA must also be looked at.

[puz_md]

Thanks for your reply. As mentioned above, I'm setting Tx power correctly which can also be observed in the extended range for advertising (compared +20 dBm to +10 dBm and compared to the nRF5340 without FEM). My point is that increasing Tx power further will not improve bidirectional connection stability if the mobile phone still sends with its nominal power, probably below +10 dBm, which cannot overcome significantly more range then Nordic at +10 dBm to the mobile phone.

[PaKa]

Yes, you are adding 17dB for the link budget in one direction and only 3 in the other direction so you may get an asymetric link. Not sure what the max power on the phones are but they do use regional awareness so even if they support more then 10dBm they should not use it if testing in Europe.