RSSI Signal Variation with Distance

[Higo]

Hello everyone, how are you? I

'm doing some communication tests between nRF52840 boards. I measure RSSI at different distances.

The problem is that in my tests, the RSSI got worse when I varied from 1 meter to 5 meters, 10 meters and 15 meters, all within expectations, however, when I went to distances of 20 meters and 25 meters, the signal started to improve.

I can't explain this signal improvement behavior when I increased the distance.

Does anyone have any suggestions?

I have attached two graphs.

I did the experiments with different PHY modes.

 

Thanks

[Higo]

 

[JONATHAN LL]

Hi, 

RSSI is not the best tool to measure distance as it will be effected by other things so location and circumstance can give samme RSSI value at different distances. 

I dont know how it is in you setup but it might be that the 20+ meters away you are at a higer point further from ground\floor. This can be a explanation to why the results starts to improve.  There might also be thigs like reflections of other surfaces or maybe there is a area where there is a lot of interference that disrupts the signal quality, moving away from that area can then give better RSSI values even if the distance is further away. 

Other factors can also be orientation of the antenna\device, the radiated field can be a lot better in one or two directions for example. 

Regards,
Jonathan