How to measure RSSI of single NRF52840 dongle or dk to another NRF52840 device?

[EdT]

I have both a NRF52840 (actually 2) and 2 dongles. I need to measure RSSI vs distance for a single link. I set up the RSSI viewer and it shows a blue or green bar for the RSSI on each of the 2.4 GHz channels. I assume I am looking at the wifi, Bluetooth, and cordless devices in the environment. But, that does me no real good. I need to set up two devices and measure the RSSI vs range between those two devices. How is this done? I am hoping that I don't have to write any code at this point in time, but if I do, if someone could point me to a sample, that would be great. I also tried loading the heart rate monitor and connecting to that with my Android phone. That works, but it only stays connected for a few seconds, until the graph is mostly drawn at 250 bpm, and then disconnects. I don't know if there is any practical way to use that. I would really like to measure RSSI between two NRF52840 devices.

[haakonsh]

See the BLE Blinky Client Application Example and BLE Blinky Application Peripheral example. Any advertisements reports that the central get from the SoftDevice will include the RSSI of the advertisement packet. 

You can use sd_ble_gap_rssi_start to get RSSI once you're in a connection. 

Although you only measure RSSI during packet reception, any 2.4GHz RF noise is going to be sampled as well, that just how RSSI works.