Testing DJI 2.4GHz datalink

by | March 14, 2019

Part of my current project involves using a multirotor UAV with a methane detection system to monitor for pipeline leaks in small high pressure distribution lines.

I first started getting involved with UAV systems back in 2014 when DJI wasn’t nearly the household name it is now. The Phantom 3 had just come out and they were still actively involved in providing airframes and flight controllers that were modular and modifiable. Their new development platforms like the M200 and Matrice 100 are very nice, and the M600 is an impressive heavy-lift system, but they aren’t as easy to tweak to non-photography workflows.

I purchased a DJI S900 and DJI S800 Evo along with DJI’s own Wookong-M flight controllers to play with custom payloads and sensor platforms. Since then I’ve mounted up cameras for mapping, photography and photogrammetry. I’ve used them to make 3D models of rock outcrops and calculate structure from those models using computer vision. Most recently I am testing a prototype methane detection system that can’t fit on a smaller UAV platform due to its weight and size.

This workflow requires the ability to fly waypoints. Much to my frustration DJI has discontinued their own PC groundstation application and provides no support for their now deprecated 2.4GHz datalink, which was an incredibly good piece of professional kit. Thankfully 3rd party ground control software such as UgCS can still use the DJI datalink to fly waypoints.

Test setup

  • DJI S800 Evo Multirotor
  • DJI Wookong-M (WKM) flight controller
  • DJI 2.4 GHz Datalink
  • UgCS Ground Station Software
  • Microsoft Surface Go ground station computer
  • FrSKY Taranis X9R RC controller with X8R airside reciever

Setting up ground station

The first challenge I encountered was the fact that the DJI drivers for the Wookong and DJI datalink are old. They were written and designed with Windows 7 and 8 in mind, not Windows 10. As such they are not digitally signed and trusted by Microsoft.

To install these drivers you must disable digital driver signature enforcement in Windows 10.  Once you are booted into Windows with this disabled it is possible to install the DJI Drivers properly.

Once the drivers and Wookong-M assistant are installled, I installed the UgCS ground station software. This is a slick piece of software that allows for waypoint flight for a wide range of autopilots including Ardupilot, DJI and others.

UgCS Ground Station

Testing procedure

My primary concern was testing the range I could expect to maintain strong telemetry using the DJI datalink. To this end, I tested my configuration in multiple locations with varied terrain and EM noise.

The first set of tests took place north of Calgary, a major city of 1.2 million people with all the electromagnetic noise associated with a city of its size. The second set of tests occured north of Macklin Saskatchewan in an open field with no major urban centers within 100km of the flight location. Finally I tested the UAV west of Red Deer in a more forested area with rolling hills.

Calgary Test

Flight Parameters

Altitude: 30m AGL

Antenna placement:

  • Ground Station: On top of truck tonneau cover
  • Air side: 90 degree polarization, vertical and horizontal mounted below the main frame of the S800

Weather: clear, 2 degrees C, mild wind

Terrain: open field, no obstructions. Cellphone tower located 1km to the east of flight path.

Results

Telemetry link reached 50% strength after 250m horizontal distance from launch location.

Telemetry link reached 25% strength after 400m horizontal distance from launch location.

Saskatchewan Test

Flight Parameters

Altitude: 30m AGL

Antenna placement:

  • Ground Station: On top of truck tonneau cover
  • Air side: 90 degree polarization, vertical and horizontal mounted below the main frame of the S800

Weather: clear, -1 degrees C, mild wind

Terrain: open field, no obstructions. Drilling rig located 2.5km SW of location.

Results

Link quality remained above 90% out to 1.0km horizontal distance. Further testing dismissed for safety reasons.

Red Deer test

Flight Parameters

Altitude: 30m AGL

Antenna placement:

  • Ground Station: On top of truck tonneau cover
  • Air side: 90 degree polarization, vertical and horizontal mounted below the main frame of the S800

Weather: clear, 6 degrees C, mild wind

Terrain: pipeline right of way, 10-15m trees on either side of flight path, minor shrubs along flight path. High voltage power lines located 800m east of flight path oriented parallel to flight path.

Results

Telemetry link reached 50% strength after 350m horizontal distance from launch location.

Telemetry link reached 25% strength after 700m horizontal distance from launch location.

Results discussion

It appears that under ideal conditions the DJI datalink is quite capable of solid telemetry out past 1000m. What is most interesting is that the terrain and weather conditions were nearly identical in both the Calgary and Saskatchewan tests, but it appears that the proximity of city communications and radio noise has a very significant impact on telemetry signal quality.

I was surprised by the results along the pipeline right of way. It appears the multipath interference caused by the trees has a significant impact on the telemetry link quality. However, it was far less pronounced than that found by simply flying near a city.

Final take aways

This post might seem a little odd. But there is very little documentation on the performance of this particular data link online. It seems it wasn’t a very popular piece of equipment for DJI and they provide very little indication of the limitations of the system beyond stating that it has a range of around 1100 feet. This testing shows that this claim by DJI is a little understated under ideal conditions, but I suspect that this range was stated due to the fact that this link may be used in urban or other sub-optimal situations.

If you either already own, or are looking at buying a used or old stock version of this data link, I hope this post helps. I firmly believe that DJI took a big step back for corporate and academic users by moving to their fully integrated A3 flight controller/Lightbridge system. Not all of us need HD video downlink and are looking to use our drones with industrial payloads.

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