Signal Strength Indication vs Signal Loss

[Chaosrider]

I've finally been able to get some flying time in, after a long work-induced hiatus. Between yesterday and today, I've flown my Mini-1, one of Mini-2s, and my FPV. Just now I got a clearer picture of something I've been seeing around the edges for a while.

Note that these comparisons are all done with flights in the same area.

With the Mini-1 and Mini-SE (slightly better with the -SE), there's virtually no notification of signal degradation in DJI Fly, before the signal actually gets lost. I can be showing 5 solid bars, and then boom...no signal.

I just finished a "signal prodding" test with my Mini-2, poking around the edges of losing bars, and seeing where the signal actually cuts out. I didn't see a single case of actual signal loss without losing at least one bar in Fly. If I'm cruising along at top speed, it can go from 4 bars to signal loss rarely, but if I'm poking along at a more stately pace, the indicator and actual signal loss have a reasonably close correlation. 5 bars, to 4 bars, then 3 bars. I hardly ever get complete sudden signal loss until I'm already down to 3 bars or fewer.

The FPV actually has two signal strength indicators, and between the two of them, I can get a very good sense of how close I am to the ragged edge of signal loss. Cruising along at Warp 6 in my seriously uneven terrain, I'll sometimes get caught by surprise, but not very often.

Obviously, this corresponds directly with WiFi vs OS2 vs OS3.

It also correlates with how much the signal cares about antenna position relative to the aircraft. The Mini-1 and the Mini-SE whine early and often if I don't have the antenna pointed correctly. The mIni-2 cares a great deal less, and the FPV almost doesn't care at all.

In my personal "Can I justify this?" calculation, I need to get the flight rate back up on my existing fleet, before I can justify getting the Avata! I should get there right about the time it starts to get too cold to comfortably fly...

;-)

 

[akdrone]

I’ve been amazed at how my FPV can be momentarily in back of me (with my spotter watching) while I sit comfortably in my chair (yeah…still need that) with no signal loss. I do wish that all of the DJI drones could use the Pro controller with it’s’ superior range. I would buy it in a heartbeat.

 

[AZDave]

I can almost guarantee that any controller has some sort of averaging function for the signal strength display, and that will cause a delay in reporting a loss of signal. The software in the controller may even assume that that you aren't watching the display every tenth of a second, and therefore update on a slower schedule in order to prioritize other functions

 

[Chaosrider]

I’ve been amazed at how my FPV can be momentarily in back of me (with my spotter watching) while I sit comfortably in my chair (yeah…still need that) with no signal loss. I do wish that all of the DJI drones could use the Pro controller with it’s’ superior range. I would buy it in a heartbeat.

I've had that same thought. Either the Pro, or Son of Pro.

I'd pay good money for a controller that worked with all DJI drones.

Not with some silly "screen below the sticks" configuration though...

 

[Chaosrider]

I can almost guarantee that any controller has some sort of averaging function for the signal strength display, and that will cause a delay in reporting a loss of signal. The software in the controller may even assume that that you aren't watching the display every tenth of a second, and therefore update on a slower schedule in order to prioritize other functions

Probably true in some sense, but that doesn't explain the Mini-1 and Mini-SE going from 5 bars to signal loss in the blink of an eye. Over exactly the same flight area neither the Mini-2 nor the FPV do that.

 

[AZDave]

Probably true in some sense, but that doesn't explain the Mini-1 and Mini-SE going from 5 bars to signal loss in the blink of an eye. Over exactly the same flight area neither the Mini-2 nor the FPV do that.

Actually, yes it could explain that. The signal display algorithm in the less expensive drones could update slower, and the display could easily update only after the signal has already gone away.

 

[Chaosrider]

Actually, yes it could explain that. The signal display algorithm in the less expensive drones could update slower, and the display could easily update only after the signal has already gone away.

Perhaps, but that seems odd. The Mini-1 doesn't go that fast.

 

[AZDave]

Perhaps, but that seems odd. The Mini-1 doesn't go that fast.

By fast, do you mean flight speed of the drone? I don't think that matters much. You can almost instantaneously lose signal strength by flying into an area where a reflection of the main signal combines with the main signal and cancels. That reflection doesn't even have to be off an object ... it could even be just a bump in the foreground, or off steep terrain to the side.

RF can be weird. I'm a ham radio operator and there are guys who have made contacts on UHF frequencies well beyond line of sight by bouncing signals off jets that are landing at an airport.

 

[Chaosrider]

By fast, do you mean flight speed of the drone? I don't think that matters much. You can almost instantaneously lose signal strength by flying into an area where a reflection of the main signal combines with the main signal and cancels. That reflection doesn't even have to be off an object ... it could even be just a bump in the foreground, or off steep terrain to the side.

RF can be weird. I'm a ham radio operator and there are guys who have made contacts on UHF frequencies well beyond line of sight by bouncing signals off jets that are landing at an airport.

I understand that generally, but I don't think it's the issue here. These are places that I've flown many, many times.

But as a result of a flight I did with my Mini-SE just now, the answer has become clear.

I've got a standard CanyonBall Run that I do pretty regularly. Today, I decided to take the -SE down the run, but at as low an elevation as I could while still maintaining signal. The results were unexpectedly revealing.

The signal strength indicator in Fly measures the strength of the control signal only. The only "indicator" for the quality of the video signal, is when the video cuts out, or actually, freezes.

The video signal cuts out way before the control signal does. And when the video signal cuts out, it threatens to go to RTH unless you cancel it. The difference is, if the control signal goes out, it just does the RTH. If just the video signal cuts out...you can still fly the aircraft!

I always have the "compass view" open in the little window in the lower left window of the Fly screen. As long as the RC signal stay strong, I can continue to control the aircraft...flying seriously IFR! I can rotate it, move it forward and backward, or raise it or lower it. It periodically whines that the video signal is out, but it doesn't say that it's the video signal only that's cutting out. It only "tells" you that indirectly, by your continuing ability to cancel the video signal loss RTH, and fly the aircraft.

I know this canyon like the back of my hand. If I know the distance of the aircraft, and the angular direction to the homepoint, I know where it is, and I know how high the terrain is under and around it.

I danced around on the edge of the video signal range for quite a while, like slow flight in a fixed wing airplane where you fly around continuously on the ragged edge of a stall, with the stall horn blaring.

Armed with this knowledge, I was able to get the little -SE out to the de facto FAA limit for VLOS, 2 km (1.2 mi, 6336 ft), while remaining within the 400 ft AGL limit the whole time.

So the mystery is solved! The reason you get a loss of signal RTH (at least on the -1 and the -SE) even when the icon still shows 5 bars, is because you still *DO* have strong control signal strength. It's the loss of the video signal strength...which has no indicator in fly...that's triggering the RTH.

Mystery solved!