Appropriate value of received RSSI

[loquat]

I use nRF Connect for desktop / Bluetooth Low Enery Apps + nRF52840-DK.

When run 'start scan', In rare cases, very small RSSI values (-103dbm, -104dbm ...) may be reported.
Is this value correct?(Is it a reliable RSSI?)

[Mttrinh]

Hi, 

According to chapter 6.20.15.9 of the nRF52840 Product Specification v1.1, the accuracy is ±2dB. For the nRF52840, the RSSI accuracy valid range is -90 to -20 dBm. If the RSSI value is outside this range then it isn't reliable. 

Just be aware that there are many factors that can affect the RSSI value, see this thread.

[Mttrinh]

It means the RSSI value can no longer be trusted.

[loquat]

For example, if the received RSSI value is -100dbm, does that mean it could actually be -40dbm or -90dbm? Or does it mean a very small RSSI value?

[Mttrinh]

If the received valued is out of the valid range, it means that the value isn't accurate and is affected by some other factor. The correct value will be something different, like -40dbm or -90dbm. 

As it is mentioned in the other thread I referred to

Low RSSI could be caused by any number of things, RSSI is simply measured received power at receiver. The cause of reduced received power cannot be read from RSSI directly. It could be mismatch in RF front-end (matching network/antenna), fading due to multi-path, obstacles, etc. 

[loquat]

OK.Thanks.