mesh light demo with nrf21540ek

[William.wei]

hi support team,

i want to confirm the FEM control when using nrf21540ek for mesh demo "light" with 52840dk.

i set :

CONFIG_BT_CTLR_TX_PWR_ANTENNA=20

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10

i expect the TX POWER register to be 8db, however i read the registor it is 0, which means 52840 is using 0dbm.

it is the same situation when i build nrf21540dk, the internal TX POWER is 0

i couldn't see why TX POWER register is not 8db.

however for demo "peripheral_lbs":  with the same settings,  i have confirmed the registor is 8.

Regards,

William.

[Edvin]

Hello,

The input to the nRF21540 shouldn't exceed 5dBm, so I assume it sets it to 0, and lets the FEM handle the rest. Hence, I think you should try to remove the CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10, because it would require the nRF52840 to have too high output power. 

Have you tried measuring the output power, and see if it changes when you set these configs? I am not certain that the register value will stay at the output level the entire time, or if it in some cases are just set directly before the device is using it's radio, and then reset directly after.

Best regards,

Edvin

[William.wei]

hi Edvin，

you should be correct:

the output power of 52840 shows the 52840 is using different tx power to send data:

CONFIG_BT_CTLR_TX_PWR_ANTENNA=10

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10

CONFIG_BT_CTLR_TX_PWR_ANTENNA=14

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10

CONFIG_BT_CTLR_TX_PWR_ANTENNA=20

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10

Regards，

William.