DJI Digital HD FPV System - FAQs, Common Issues and Tips
With expressed permission from Oscar Liang, we are reposting this article to answer some the questions you may have regarding the new DJI Digital HD FPV system.
Air Unit Has Different MMCX
The DJI antennas have longer than normal pin in the MMCX connector – that’s why when you buy antennas for your Air Unit, you should get those specified for the DJI Air Unit.
Interference to 5.8GHz Analogue
As the DJI FPV system also transmits on 5.8Ghz band, it will interfere with analogue if the channels are too close. This is worse if you use 50Mbps mode as it uses a much wider band. If you wish to have less issue, try to stay on 25Mbps and a lower power such 200mW or even 25mW.
RSSI for DJI FPV System
There is no RSSI measurement for the DJI FPV system, however you can look at the signal bar (at the bottom left), and the bitrate (aka bandwidth at the bottom right) for signal strength.
Can You Get Signal Back After Losing Signal
It can take around 30 seconds before the reception comes back (applies to both 25Mbps and 50Mbps), So it’s pretty unlikely you can get signal back after losing it as you will probably crash before it does. that’s another downside vs analogue FPV system.
Setup GPS rescue perhaps, it can buy you more time, even bring the drone back home.
Selling and Unregistering
Do I need to unregister DJI FPV products when I want to sell them?
DJI FPV Goggles
4:3 or 16:9
What aspect ratio do you fly with? 16:9 or 4:3?
I personally fly 4:3 because you get an image of the whole image sensor. In 16:9 it simply cuts off the top and bottom portions of the image and so you have less vertical field of view.
With full sensor 4:3 image, you can also create superview videos with the recording footage.
What Battery To Use with DJI Goggles
4S 1600mAh provides about 3.5 hours of battery life.
You can use any 2S to 4S LiPo or Li-ion batteries. C rating doesn’t matter as it doesn’t draw many amps.
Personally I just use an old 4S LiPo for my FPV drones (e.g. 4S 1500mah), or you can just get any cheap and basic 3S or 4S packs online, pick the biggest capacity you can afford and carry.
Power consumption is almost 8W, that means a 4S 1500mAh battery lasts about 3.5 hours.
As expected, the Goggles will beep (voltage alarm) when battery voltage drops below 3.5V per cell, that’s 7V for 2S, 10.5V for 3S and 14V for 4S. This is great for LiPo battery, not so much for Li-Ion as this is only half way discharging the battery and you’d get this annoying beep. We have the same issue we get using Fatshark goggles.
That’s why I’d avoid using 2S if you power analogue receiver from the same battery, the battery voltage would drop more and trigger the alarm even earlier.
I tested the goggles with a power supply with adjustable output voltage, to see what the minimum voltage the goggles support.
- Below 7V, the goggles start beeping (voltage alarm)
- Below 6V, the fan stops
- Below 5.8V, the bitrate becomes unstable and dropping
- Below 5.5V the beeper stops, and connection to Air Unit is gone, but the screen is still on
- At 5V the screen shuts down
So I think 6V is probably the bare minimum I’d run the DJI FPV goggles.
LHCP vs RHCP Antenna
Should I choose LHCP or RHCP antennas?
These are the circular polarization directions, you can use either type as long as they are the same on both DJI goggles and Air Unit.
I personally prefer LHCP because that’s what the stock DJI antennas are. If you use RHCP on your goggles, you’d have to replace the Air Unit antenna to RHCP as well.
How to Mount Directional Antennas
Follow instructions and recommendations from your antenna manufacturers, but if that’s not mentioned in the manual, you can try this.
The top two antennas are for both transmitting and receiving data, while the bottom two antennas are only for receiving. Therefore, put your directional antennas on the top connectors. The system will only go as far as it can maintain bandwidth in both transmitting and receiving.
In my experience, the bitrate of recording in FPV goggles is normally between 30Mbps – 40Mbps. Very rarely it would drop in the 20’s, but it’s possible.
Setting transmission to 50Mbps in the FPV Goggles doesn’t seem to affect DVR bitrate which is in the same range for both 25Mbps and 50Mbps modes.
Do DJI Goggles Transmit When Running Analogue Receiver
DJI FPV goggles only start transmitting signal when they see Air Unit, until then the goggles are receive only. Transmission power will ramp up when a two-way communication is established.
Analogue Signal Gets Low and Goggles Reboot Blue Screen
When using analogue receiver with DJI FPV goggles, and signal gets low, they reboot and show blue screen. This is most likely caused by the FPV camera in PAL format, though some receiver modules work just fine even with PAL cameras.
The easiest workaround is to switch your FPV camera to NTSC if the option is available in the settings. Otherwise you might have to swap the camera out for an NTSC one.
Small Dot On Screen – Sun Burn
If you have a dot on your screen, that’s likely to be a sun burn, which shows up as green circles. It’s unlikely to be dead pixels, as they are very hard to observe with naked eyes because a pixel is extremely tiny. So if you get a small dot on the screen that’s noticeable, it’s probably many times larger than a small, rectangular pixel.
It only takes a second or two to burn your screen with bright sun, so make sure when you put the goggles down, turn them over to face down.
Slow SD Error
If you are getting “slow SD error” in the goggles, here are the possible fixes:
- Get the correct SD cards with decent read and write speed
- Format the SD card inside the goggles (via the menu)
- Another trick to avoid this error is to start recording manually when the quad is still (not moving), let it record for a second or two before arming. This is because when the quad is moving, the image moves too, and the bitrate (data burst) can be too much for the card to handle
- The other possibility is that you might have a fake SD card. Clones of Micro SD cards are quite common even in retail. Test SD card speed to verify
- Update to the latest firmware
Corrupted Video Files
You could corrupt the video files either when you crash and the battery disconnects, or you unplug the battery while its still recording. You might not be able to play or edit a corrupted video on a computer.
The easy fix is to put the SD card back into the goggles (or air unit), plug in the battery, wait about 10 to 15 seconds and then unplug it. The Air Unit will scan the SD card and fix any corrupted files. You can then put the SD card back in your computer and the file should be good.
To avoid corrupted video files, make sure you wait a few seconds after the recording has stopped before plugging battery.
Missing Channel in 50Mbps Mode
50Mbps takes up two channels, so only channel 1, 2 and 3 channels are available (plus a public channel 8), instead of the original 8 channels.
If you only see channel 1 and 2, but missing channel 3, you can try a factory reset to default settings, that should sort it.
Best Settings for Low Light and Night Flying
All camera settings are in the goggles, just adjust the exposure in your goggles. Use the LED mode for night / low light flying.
SD Card Full Error
If you are getting SD Card Full error in the goggles, but in fact there is still space on the card, and your DVR recording stops at around 14 or 16 mins long every time, this might be an issue with SD card formatting.
Just format the card inside the DJI goggles using the menu, this should fix it.
DJI Air Units and Caddx Vista
How to Power Air Unit
From a BEC with 8V, 9V or 10V output voltage, capable of supplying 1A, or even better 2A of current. You can power it directly from a 4S LiPo, but the Air Unit doesn’t like electrical noise and voltage spikes, if you insist on powering with raw voltage, make sure to add a big low ESR capacitor.
How to Power Caddx Vista
I’d recommend similar practice to the DJI Air Unit (power from a BEC), despite the fact that the Vista can take up to 6S input voltage. Vista doesn’t like voltage spikes either, in fact it’s a common issue that voltage spikes fry the diode in the serial port, and leaving you without OSD.
But if you want to power it directly from a LiPo battery, make sure you add a big low ESR capacitor, because if power gets too noise it can freeze the video too.
Bricked Air Unit
If you accidentally disconnect the Air Unit (or Caddx Vista) during firmware update, or the update fails during update, it could brick the Air Unit. It won’t appear in DJI Assistant 2 anymore when you plug in the USB cable.
To resolve this, you will have to contact DJI Support, send them the update log and a screen shot of the error code.
Low Power Mode
If you are getting “Low Power Mode” indicator on the screen, it’s not a warning, it’s just standard for the VISTA when the drone is disarmed. After you arm, low power mode would be disabled.
Black Screen But Still See OSD
That’s typically the camera cable popping out just on the Vista / Air Unit side. This happens more often with the Vista, the cable may pop out after hard landings or crashes. To avoid this from happening again, try using some liquid tape on the far edges of where the cable locks into the Vista, because the small black clamps aren’t very strong and the metal holder bracket doesn’t do much.
Vista OSD Stops Working
Getting video but no OSD?
The problem is that people are powering the Vista directly from battery, and voltage spikes could damage the diodes in TX/RX (serial port) and SBUS. To avoid this issue, best to power your Vista with a BEC (e.g. 9V voltage).
When this happens, the diodes are shorted to the ground, you can confirm by checking continuity with a multimeter between the TX or RX pad with ground.
If this is indeed the case, contact DJI or vendor for repair, or, I’ve heard you could just remove those diodes, and that would fix it but do so at your own risk.
DJI FPV Remote
How Long Does It Take to Charge Battery
Roughly 10 hours, it’s a big battery.
What’s DJI FPV Remote Stick Thread Size
It’s M3 if you are looking to replace the stick ends.
Polarization of the Remote Antennas
I have not tested it but some suggest the antennas of the DJI FPV remote are slightly LHCP, something to be aware of when changing Air Unit and Goggles antenna to a different polarization.