@LutherBlisset (and others who are interested)
You can easily make some basic experiments if you have access to two mobile phones. Use an app such as “nRF connect” that does basic BLE stuff, and that will show you all BLE devices that are scannable in the area. The app also lets you set up an advertiser. (Basically a BLE beacon. Can be seen and scanned by other people in the area)
Set up one of the phones to be the advertiser. Set it to display its “Complete Local Name” (which you could change). This will help you find it on the second phone, which will use the scanner. The scanner will let you define a filter, where you can input the name of the advertiser so that there is only one device in the list.
The advertiser. Click the EDIT button to make it display “Complete Local Name”. If you wish to change the complete local name, click the pen in the top menu and enter a new name. Otherwise it will just be your phone model.
The edit screen. Click the “ADD RECORD” and select “Complete Local Name”
Then slide the slider on the first screen to turn on your beacon.
Then use the second phone. Open the same app, and select the SCANNER screen at the top. Click SCAN. Stuff will start appearing (how much depends on how many BLE and Bluetooth devices you have in your home). You should find the Advertiser that you set up on the first phone in the list. If you have a long list, you can use the filter function to filter by name.
Look at that! I see my phone. It has a -71 dBm RSSI. (Unfiltered list)
Now you have a setup to experiment with. One thing that is quite noticeable, is that a human body between the phone changes a lot. With one phone on the table and one in my hand I see something like RSSI (40 cm distance) I have around -60 dBm. When I put one phone behind my back (between me and the backrest of the chair) and hold the other in my hand in front of me (about the same distance) the RSSI drops to between -80 dBm and -85 dBm. If we saw that kind of a difference in free-space transmission we would conclude that in the second setup the phone was 10 to 17 times as far away. So for example, a phone in a back pocket will seem farther away in a face to face meeting. And if we walk side by side there is a big difference between a phones in the near pockets, or phones in the far pockets.
(d2/d1 = 10^((Pr1-Pr2)/20) where d2 and d1 are the distances, and Pr1 and Pr2 are the RSSI values in dBm for the two measurements.
(You may have to twiddle the Advertisement type in the setup. Only one of the phones have Bluetooth 5, so I had to set advertisement type to legacy if I wanted that phone to be the beacon. If you struggle, set the older phone to be the beacon, and use the newer for scanning.)
Go forth and play! (In a socially distancing way, of course!)
