DJI Digital FPV System - Ocusync On A Spectrum Analyzer
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- Опубликовано: 7 июн 2021
- Taking a closer look at the DJI Digital FPV System on a spectrum analyzer, specifically the Aim-TTI PSA6005. We look at the behaviour of the Air unit, goggles V1 and V2 and DJI FPV Remote and show its behaviour on 25mbps and 50mbps modes..
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very very interesting.
can you analyze the DJI FPV DRONE system in similar way ?
I have been testing but I will show it soon.
Thank you. Seeing the traces really helped me to understand what is happening
Proper job, watching now and enjoying it. Chair and posh desk in one video!
A VERY good analysis of the rf use of these units, thanks!
Thanks
Full on man love it. Good job man
thanks so much for the email about my Nazgul black box appreciate it big time
amazing detailed proof video. tks again :-)
Thanks for the detailed analysis. We have plenty of DJI flyers and this is what we have observed
1. On 25mbps, no problems. If a new user switches on the same channel, it remains in 8 till the new user selects a new channel
2. On 25mbps, if a user switches on at 50mbps, there is a good chance of loss of video for the flyer on 25mbps for at least 10 seconds
3. On 25mbps, if a user switches on a new DJI FPV Drone, again there is a good chance of loss of video for the flyer on 25mbps for at least 10 seconds
We currently don't let anyone fly on 50mbps or with an FPV Drone unless they are the only one flying as it's a bit of a lottery depending on what channels they are on.
Great Information provided about the DJI V2 goggles.. I deal with Frequencies and Spectrum daily designing wireless networks. Chanalyzer is great software with Wi-Spy hardware.
thats really cool. ive wondered how the system works and this gives a good picture. also means that you can leave the controller or goggles on longer and they won't drain much power if the air unit is off.
shark byte would be far less complex but still interesting to see, yet perhaps it would look just like an analogue vtx on the scope
great video
Great in depth review!
I was working in the high frequency industry (80Ghz for automotive radar sensor)
Great coverage!
Also would be interesting to analyse the fpv combo system
It changes a bit but it’s very similar on the FPV Drone but I will be doing one the same. It looks very similar overall apart from remote stays on 2.4ghz almost all of the time regardless of what video is doing.
Very interesting! Thanks for the info! Couple thoughts on some further testing - Perhaps try repeating these power on tests with another DJI FPV system present and see how things behave (and perhaps put some distance between quads to simulate someone powering on whilst another flying). Then try an analogue system set on DJI channel 8 - perhaps the added noise floor would cause the DJI system to move the telemetry around? Also it'd be interesting to see some comparison of the FPV system to the DJI FPV drone's RF behaviour.
i read somewhere when switch from 25 to 50 we need to reboot the goggle or the air unit.. maybe after reboot we can get that telemtry for rc link on top of the video channel as on 25mb mode.
Very cool! Now to drag out my spectrum analyzer that I've never been able to figure out how to use. Neat stuff they are doing, with the frequencies, power and all. Is this sorta similar to what 3DR was using ??? I have a truck load of 3DR stuff, that still intrigues me.
Thank you for this Information. It helped me a lot with my SDR. I experienced a bit other behavior with my dji mini 2 with ocusync 2.0. The OFDM Carrier (h.264 Video) is changing the Channel when there is another interfering signal. This often happens in the 2.4GHz Band. After some hops in this noisy band it switched to 5.8GHz. Also the Control Signals (those Spikes) are randomly jumping around in the band. I hope that will help someone.
Interesting Ian ... btw, what's the drone you have there? looks solid ... ¶ ;-)
I have knocked a fellow pilot ouf of the sky. The reason was he was on 25 mW and I was on 700 mW. Even though we were on seperate channel, at the very moment I powered on the quad, he lost video immediately. So be careful and make sure you are using similar output power even if on 25 Mbit/s and on different channels. This happened twice. Him switching to 500 mW fixed it completely and we were flying happily even in close proximity to each other.
Great video! Did you use the goggle v2 in this video?
It’s identical behaviour on the V1 and V2 with Airunits. Nothing changes as it’s the same setup.
Be very interesting to see what happens with the Mavic 2s.
I have shown the Mavic 2 on the live stream, overall very similar behavior. its all OFDM
I’m quite intrigued about the comms you say is happening between goggles and controller directly. This kind of seems a bit ‘odd.
The reason is simple : many of us don’t use the controller but a different tx/rx eg I use crossfire.
In this configuration, obviously, there is not controller/goggles comms - the telemetry in the goggles is from the flight controller/aircraft , and I’d assume is ‘mixed in’ with vtx ( it’s digital so no issue with doing that) .
I’d guess the only goggle/controller telemetry that’s useful is the tx side. Or for anything that’s a controller function ( but not sure the dji controller has anything like this , compares to say opentx)
Interesting, do you think the separate video and telemetry in 50Mb mode is a bug? Also we’ve found at our club that the first time someone plugs in their headset and air unit that it can blast analogue out the sky, but interestingly, as long as you don’t power off your Google’s, you are then safe to plug-in the air units willynilly without blasting analogue out the sky once the first power up is done.
I think its desired behavior but i think its capable of following, im guessing they want to keep it clear for the best possible video bitrate.
Should have been in my last comment, but it would really help me to see an analog system
I will show more on this soon.
I’ve very recently acquired the Amimon Prosight system as supplied with the Connex Falcore. I’ll be sticking it on my Spectrum Analyser as I’m curious to see if it truly is as dynamically frequency agile as Amimon claimed it was. They also claimed a low probability of interference to other colocated users so I’ll check this alongside my analog systems. One day I might get round to flying something 🤣. I highly doubt it’ll be using OFDM like the DJI system is as OFDM cannot dynamically switch frequency fast enough without incurring appreciable interruptions in the video feed. It will be interesting to see how it actually does administer dynamic frequency management.
Yea, no one I have seen has done channel hopping video well, while Ocusync can change channel and band its in the event of interference and its noticeable for sure. .
@@MadRC And neither have Amimon. I've just had the system on my analyser and it's the same OFDM technique as that used in the DJI system but with a smaller bandwidth of around 12MHz (it supports 720p @ 30fps and 60fps. However it does do an operation similar to LBT when frequency management is set to Auto. The latency is also near undetectable @ about 20ms. The version I have seems to be the American one as it's switchable up to 200mW where as the European version was limited to 25mW according to Painless360's review. It's quite flexible though as it supports S-Port, Mavlink, and Naza/Wookong/A2 telemetry, but for some reason didn't stand the test of time.
Interesting stuff. would be enlightening to see if DJI kept the same behavior for the DJI FPV drone - or did they tweak it?
( also useful if DJI FPV drone flyers are around others. )
It changes a little on the FPV Drone but I will be doing one the same. It looks very similar overall apart from remote stays on 2.4ghz almost all of the time regardless of what video is doing. The drone behaves more like Ocusync on Mavic series
@@MadRC interesting.... does this happen if you force it to 5.8 ghz? Reason I ask, is if you also use the air unit , and have fitted 5.8ghz antennas to googles ... does this cause issues?
( assuming you are forcing to 5.8ghz mode?)
I plan to do some practical range tests in next few days, but would be interesting to juxtapose this with the ‘theory’
I have been shot down by a analog FPV user and the googles seem to go into some form of fail-safe/emergency mode and it seems you have to reboot the air unit before things are back to your settings.It looked like it went to 25mw mode ignoring my 200mw setting. Just turning the analog FPV user off does not fix it. Would be nice to see what is going on. Thanks
Is it possible that in 50 mb if there’s already an other system on, the radiocontroller frequency shifts together in the selected channel rather to stay in 8?
Yes, its predominately stays on 8 in my tests but I do think its capable of moving but its not default behaviour like in 25mbps mode where its clear. II am going to do some more testing on this specifically
What about V2 goggles, as they are dual band would be interesting to see how the signal is spread?
It changes very little on the FPV Drone but I will be doing one the same. It looks very similar overall apart from remote stays on 2.4ghz almost all of the time regardless of what video is doing.
Interesting video. Surely blasting ~1W for several seconds during power on is very bad RF manners, if not outright illegal in the EU? Can you think of a plausible reason for DJI doing this?
No. Honestly I can’t. It’s a strange one
i think it is about a possible loss of link or momentary power loss scenario.
although we power up our goggles (and dji transmitter) and AU very close to each other and there is no need for full power handshake, there are scenarios where you could have lost the data (up) link whilst flying. or you can experience a brownout during flight.. in both cases the AU loses telemetry from the ground and does not know how far away it is, in order to tell the ground unit(s) it is still/again active and initiate a new handshake it should blast at full power to get a signal to the ground unit(s) and re-establish a connection on the guard channel (ch8) and get the system back on the correct channel and power setting...
if you were flying near the maximum range of 1200mW and loose the connection, you will never regain connection if the au sends the handshake signal on just 25mW, so it has to blast at full power on the guard channel (ch8)
this also explains when people flying concrete bandos and long range flyers experience when they loose connection the get a few seconds of black screen, then a low res/blocky video, see the screen be re-written (by the horizontal moving lines over the screen from up to down) get a crisp image again and after that all happened a second or two later accurate osd info.. and anyone flying on ch8 gets very bad video or failsave.
17:10 looks like it's 15dB stronger on boot, this would be approx 800mW
When looking closely on my end it’s between the 800 and 1200mw. Imo it’s fully output when testing on the bench.
@@MadRC yeah depends if you are looking at peaks or troughs. Not that a few dB makes much difference anyway 👍 great insight m8
Ahhhh.... no wonder why when i'm on ch 8 analog, my mate powered up I get KO'd for a few seconds!