SX 868 DevKit (XK8X-DMS-0) has -40dbm @ 5 cm distance


during my first tests with the SX 868 DevKit (XK8X-DMS-0) i got -40dbm in the range test while both devices had only a distance of 5 cm. I would like to know, what i did wrong because this value is for my understand way to bad.

With the same setup i performed a test over 2.4km with an result of -82dbm. I don’t believe that the ~13 km are possible with this and i my guess is, that the -40dbm in the close setup shows already the problem.

My Question is: Why do i have -40dbm in this small range and how can i reduce this? What do i need to change, to get the 13km to work?

Thanks for your help.

%% Current config
All default except: BR - 10kbps
And the changes were done according to page 24 of the guideline.

The -40 is the loudest value that the RSSI can report. That is due to the ADC line being used and it being set up to read the quieter levels or signals. So you would need to move the devices farther apart and reduce the power level in order to reduce the RSSI value.