How is the RSSI measurement is generated (end to end)

[Yahel_Wiliot]

Hi, I want to use Friis formula to calculate the expected RSSI value I will measure from 1 meter in 2402GHz using nrf52840 in a chamber. The Tx output is -32dBm.

When I used the formula, I got a much lower value than what I measured (measured -58dBm, calculated -72dBm).

My question is what is the process of generating the RSSI measurement from the mounted antenna to the value published at the end? is there any software manipulation (some sort of conversion formula from the the hardware measured value to the value that is advertised for the received packet)?

I read the RADIO 2.4GHz chapter and found no clew about that. Also the parameters I plugged to the formula were double checked with the manufacture.

Thanks.

[ketiljo]

Th RSSI is a value that's measured at the input if the demodulator. So a measure of the energy of the received signal. Your calculations are correct, at 1 m distance, there's 40 dB loss. But the unknow factor here is the antenna gain on both sides. If the chamber isn't fully anechoic, you will have reflections as well that will increase or decrease the signal strength (fading). 

So the 14 dB difference you see is most possibly antenna gain and / or fading.