So I took a test flight yesterday for my spare 2.0 cube on open solo and then decided to also gather some distance vs. signal data (plots attached).
I flew out from home point to 1500 m (5000 ft) at about 45-50 ft agl and returned at 80 ft agl (my RTL was set to 80 ft). I first flew out with the stock 3DR omni antenna and then repeated the flight using Alpha antenna. The tlogs were downloaded using WinSCP, exported to a text file using Mission Planner, then I parsed and pulled only the data I needed (simple process from a utility, I'll find the link for it). The distance values were calculated using a 3D distance formula:
d=√[(x2-x1)^2+(y2-y1)^2+(z2-z1)^2]
It was pretty straight forward since I found that the dx, dx, dz values were recorded in a mavlink parameter which meant I didn't have to convert lat/lon into decimal degrees and the home point was referenced to (0,0,0) which simplified the distance formula to:
d=√[(x2)^2+(y2)^2+(z2)^2]
I believe 'remrssi' is the remote rssi from what I've found on the interwebs. There is a conversion to go from the unlabeled (this is really really annoying to me) rrmrssi values to dBm but I have not discovered it as of yet. Supposedly there is documentation somewhere.
In both test flights I never lost radio connection with my controller, however, video did cut out before reaching my maximum distance. I attribute losing video to a loose HDMI cable connection on the board (I took the solo apart the night before and didn't double check). When I reached 1500 m (5000') out, I hit RTL button and let the solo find it's way back to me. I should note that when I hit RTL the solo stayed in nearly it's same orientation as when I flew out.
Nothing surprising in the results in regards to the relationship between signal attenuation and distance. There appears to be an anomalous dip between 600-900 m on the return flight for both cases which could be local noise. At 900-1000 m rssi appears to flat line, which could mean that it's dropped below a measurable level, radio is dropping more packets, and/or signal to noise is less than 1. The flat lining might be responsible for an "apparent" dip Not certain on this, still trying to understand it. There could be natural interference sources in play as well (haven't taken a magnetometer out there yet).
Next test is to fly at a higher altitude where I suspect I will get less natural interference from the ground as well as multipathing.
-I apologize for the Excel (cringe) plots. I was at home having breakfast while I pulled data so blame it on convenience and tools available. I won't do it again ... Unless it's another pre-work, breakfast analysis!