Questions on nRF54LM20A TX Power Control and nRF21540 Gain

[Louis Chang]

Hi Sirs

We are planning to use the nRF54LM20A/B together with the nRF21540 FEM in our design, and we have a few technical questions regarding TX power control and FEM gain behavior.

 

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[1] TX Power Control vs Temperature

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Is it possible for the nRF54LM20A to adjust TX power dynamically at runtime based on temperature?

 

For example, we would like to implement a temperature-dependent TX power control strategy such as:

- -20°C → TX power = 8 dBm

-   0°C → TX power = 6 dBm

-  25°C → TX power = 4 dBm

 

Does the nRF54LM20A support this type of runtime TX power adjustment?

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[2] nRF21540 Gain Observation

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We are currently testing an nRF21540 DK.

 

Under the following condition:

- Frequency = 2402MHz

- MODE = 0

- Input to TRX ≈ -1 dBm

 

We measured:

- ANT1 output ≈ 15 dBm

 

Could you help confirm whether this gain (~16 dB) corresponds to the default gain setting of the nRF21540?

If so, could you clarify:

- What is the typical and maximum gain of the nRF21540?

- Whether the default configuration uses the maximum gain or a reduced gain setting?

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We would appreciate your guidance on these questions.

 

If needed, we can provide additional measurement data or setup details.

 

Best regards, 

Louis Chang 

RF Engineer III

[Carl Richard]

Hello Louis!

Thanks for reaching out! 

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[1] TX Power Control vs Temperature

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This should be possible. You can for example check out the Automated Power Control sample and see if that is a good place to start.

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[2] nRF21540 Gain Observation

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Given the test conditions you are presenting this seems like a lower value than expected. It should be closer to 19 dBm. Which version of the nRF21540 DK do you have? If it's older that revision 2.0.0 the performance could be affected by anomaly 7 in the errata. I will investigate this and answer your other questions tomorrow.

Best regards,
Carl Richard