I tried to test range between nRF52840-DK to SmartPhone with nRF Connect.
The firmware project I flashed to the nRF52840-DK is "ble_app_proximity_pca10056_s140" , TX_POWER_LEVEL (+8)
After DK is connected to the SmartPhone I moved away with the SmartPhone for about 15m and the connection is failed,while I Approaching again they reconnect.
I expect to get at least 300-400m and not 50m , I`m doing it with two board and the results are same.
I expect to get at least 300-400m and not 50m
Are you testing indoors or outdoors? I will only expect 300-400m when doing line of sight measurements outdoors and not for indoors measurements.
Every single indoor enviroment is different so is also extremely difficult to give an estimate of the expectated range indoors, but in general you could expect a range somewhere between 10-20 m indoors using 0dBm output power.
I must say 15 m sounds a bit on the lower side when using +8dBm output power but again it could be that you are testing in an extremely poor enviroment. You should think about what obstacles are between the two devices, what are the devices sitting on and also how much 2.4GHz traffic is in the enviroment from before, there are several variables here that could explain this poor range.