nrf52840 rssi measured value

[andreaaza]

i'm trying to get distances between nrf52840 ble transmitter and receiver, using measured rssi upon receiving ble_gap_evt_adv_report_t from ble stack.
in order to calculate link budget losses i need to know if that rssi value is given in dB or in dBm .

i also would like to know which is the default value for tx power if never set using sd_ble_gap_tx_power_set(uint8_t role, uint16_t handle, int8_t tx_power), when advertising with nrf52840 dongle. ??

[Edvin]

Hello,

The TX power is the value in the radio's TXPOWER register. At least on the 51 this is by default 0. I believe it still is, but I haven't checked.

You can test by not using sd_ble_gap_tx_power_set() and check this register after starting the softdevice on your nRF52840.

In the adv_report event you can check the received RSSI strength through:

ble_gap_evt_adv_report_t->rssi (int8_t).

Note that the received RSSI value may change with the orientation of the transmitter and the receiver, the antenna, and the layout. You can check with your DKs or your custom PCB, and see how it behaves. Just know that the received RSSI may be different for a different type of device.

Best regards,

Edvin