Can't set TX power NRF5340 audio dk

[Hejdern]

Hello!

I'm trying to change the output TX power in the nrf5340 audio dk. I'm setting:

CONFIG_BLE_CONN_TX_POWER_NEG_40DBM=y

CONFIG_BLE_ADV_TX_POWER_NEG_40DBM=y

I do this to compare with the default 0 dBm setting. I'm running version 2.6.0 and using the BIS broadcast mode. The above doesn't show any change when measuring RSSI at a given distance.

Is there another setting I need to do in order to control the output power?

Thanks and regards,

Henrik 

[ovrebekk]

Hi Henrik

As of v2.6.0 of the SDK the LE Audio application no longer uses a special Bluetooth controller for audio only, but now uses the regular SoftDevice controller. As such the method for setting the TX power is the same as any other Bluetooth application, as described here.

The old configurations should have been removed, and we will make sure to remove them in a future update to avoid this confusion. 

Best regards
Torbjørn

[Hejdern]

Thanks! That worked out well! I edited the child_image/hci_ipc.conf file and then it worked.

I'm about to try out the nrf21540 FEM and I read in the docs:

"When you build the nRF5340 Audio application with the nRF21540 FEM support, the LE Audio controller for nRF5340 does not support the +20 dBm setting. This is because of a power class restriction in the controller’s QDID."

Is it certification-wise ok to use +20 dBm for a LE Audio Broadcast, or where does this limitation come from? Is it a nrf5340 issue or something else? (We are looking into a Broadcast project and need to understand the limitations)

/Henrik

[ovrebekk]

Hi Henrik

The SoftDevice controller should not have any such limit, no. Just be aware that going up to +20dBm is only allowed in certain regions (including the US). 

Best regards
Torbjørn

[Hejdern]

Tack Torbjørn!

[ovrebekk]

Hi Henrik

A quick correction to my earlier response. 

While there is no technical limitation preventing you from going to 20dBm in LE Audio applications, it is unclear at the moment if we have a QDID covering the nRF5340 + nRF21540 running the SoftDevice controller, allowing you to qualify an LE Audio design running at 20dBm. I need to look into this a bit further and get back to you. 

Best regards
Torbjørn