The signal bar in DJI’s FPV Goggles is sometimes unreliable, I found bitrate (some call it bandwidth) is a much better signal strength indicator. If you use Crossfire, you can also display LQ in OSD although it’s not yet supported.
The Better Signal Indicator for DJI FPV System
When flying with DJI FPV system, there are “signal bars” at the bottom left corner of the screen that is meant to show you how strong the video link is. However it’s not always reliable and sometimes flashes red way too early. The general consensus is to look at bitrate (some people call it bandwidth) which is located at the bottom right. In a nutshell, you should watch out when bitrate starts dropping, and you should probably turn back when it drops below 10Mbps.
Unlike analogue, the image quality of DJI FPV system doesn’t degrade gradually with weakened signal strength, when you realize you are about to lose signal it’s normally too late.
Bitrate normally stays unchanged when the video link is working correctly. Sometimes when you pop behind a tree, and the number might drop a little for a second, which is to be expected. When you are on the edge of losing signal, bitrate would stay extremely low. If you continue to push it, you will get a DJI logo and lose video feed completely.
You DO NOT want to lose signal with the DJI FPV system, because it’s unlikely for signal to come back before you crash, as it could sometimes take up to half a minute. That’s why I think setting up GPS rescue could be useful, as it can buy you more time to stay in the air, or even bring the drone back home if you are lucky.
That’s why it’s very important to keep an eye on Bitrate.
When signal bars go red, you should start watching Bitrate closely. But don’t read too much into red signal bars alone (unless it happens very close by, you might have a bad antenna in the Air Unit or goggles). As long as bitrate is still full, you should be fine at this point.
When bitrate drops below 20Mbps, you are now losing quite a bit of performance and you should be paying attention. When it hits 15Mbps, you should definitely consider to turn back! It gets extremely sketchy below 10Mbps and you could lose signal in a heartbeat.
Displaying LQ in DJI FPV Goggles
LQ as an element in Betaflight OSD, is still not yet supported in the DJI FPV goggles. However we can do this workaround to display it on the screen. Just follow the old method by passing the LQ value through an AUX channel, assign this AUX channel as RSSI in Betaflight, and finally display this RSSI value as OSD, but in fact that’s our LQ value.
Note that because LQ is a number between 0 and 300, but RSSI is a value between 0 to 99, the LQ will get stuck at 99 most of the times. That’s normal, because LQ is normally way higher than 99, and that’s why it’s “stuck at 99”. But when it drops below 70 you should probably turn back as this is the lowest safe number.
This video shows you how bitrate changes when it’s running out of range.