A default gain of nRF21540 FEM from the factory in a simple configuration

[Lukáš]

Hello, 

Sorry to bother you with this kind of question, but for us, the product specification of nRF21540 is really confusing and hard to read. Could you tell me, what is the default TX gain used in the nRF21540 default configuration?

Setup:

• Mode pin - left floating
• UICR - not programmed, left at default values
• FEM controlled via GPIO pins (not SPI) - only TX, RX and PDN is used
• TX_gain register not changed

Thanks a lot for the clarification!

Lukas

[run_ar]

Hi,

The mode pin is used to choose which of the pre programed gain settings should be used so I do not think you should leave this floating. See link to tx power setting below, you can choose between two settings:

POUTA_PROD (20 dBm +/- 0.5 dB)

POUTB_PROD (10 dBm +/- 1.5 dB)

https://infocenter.nordicsemi.com/pdf/nRF21540_PS_v1.0.pdf?cp=6_0_0_0#%5B%7B%22num%22%3A28%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C85.039%2C593.298%2Cnull%5D

[Lukáš]

Hi,

The main reason for asking was that we didn't see the 20dBm or 10dBm on the output. However, it was for a different reason (we messed up timings in the Zephyr controller). Now it works as expected - when the mode is grounded, it is 20dBm, and otherwise, it's 10dBm. It is also true that that mode shouldn't be left floating.