The manufacturer of the ground control station claims a 20 km range. We wanted to verify that was true considering the integration of our systems.
The Test Case
Verify that the drone will respond to user inputs at a 20 km range using a SwitchBlade-Elite with the standard Herelink ground control station. Determine to which distance the video stream is usable.
Requirements: Conditions needed to perform the test.
- 20 km direct line of sight
- Per FAA rules, must maintain visual sight by pilot or a visual observer
- Unrestricted airspace
- Clear day, no wind, no precipitation
How the Test Was Performed
Selecting a Location
We determined that the best location to perform this test was over a long lake because it offered a flat surface with no interruptions in line of sight. The airspace was also not regulated. The beaches and launching points were lightly trafficked and therefore ideal for safety.
Team Roles
The team consisted of three people:
- One individual drives the boat and records the test data.
- A pilot controls the aircraft, communicates with the observer, and reads data from the controller.
- A visual observer stayed with the aircraft on the beach and relayed observations to the pilot.
Equipment
- SwitchBlade-Elite 2.0
- Herelink Ground Control Station
- Indefinite Flight Package (IFP)
- Aluminum motorboat
- Vehicle and boat trailer
- Notebook and pencil
- GPS device
- 2-way radios and cell phones
- Sunshade, chairs, cold drinks
Performing the Control and Telemetry Range Test
We rented a small motorboat and trailered it to the lake. The beach we had planned to launch from was unoccupied. We unloaded the equipment, set up the canopy, and then started setting up the SwitchBlade.
Test Conditions
Temperature: 27° C
Density Altitude: 6,000 feet
Weather: Clear and sunny. No wind.
Drone Height: 1 Meter above lake level
We set up a platform to get the SwitchBlade off the ground and ensure line of sight as the boat got farther away. We also wanted a clean area to set the camera on and test the video feed.
Once the controller was connected and the camera was streaming, the pilot and boat operator took off in the boat. For the initial set of tests, the drone stayed safely on the platform. As the team moved away from the drone in the boat, they watched the video stream to determine at which distance the stream started to degrade.
Test Results: Signal Verification
From prior tests we knew the signal was nearly immutable in most environments up to 3000m. So the test was initiated at a 3000m starting distance. The pilot launched the drone and climbed to 100 meters AGL. This altitude was selected to ensure the curvature of the earth was well out of play, ensuring a direct line-of-sight to the GCS.
Measurements were taken within the Herelink controller. The values were recorded as decibels per milliwatt on a logarithmic scale. The Herelink amplifies the signal the further the vehicle is from the source. Therefore, the numbers are negative because they represent the amount of signal being amplified.
The results of this test also challenged our assumptions that a signal of less than -90 dbm would be unusable. To the contrary, the Herelink and drone communicated well between the range of -90 dbm and -130 dbm.
| Distance (Meters) | Signal (-dBm) |
|---|---|
| 3000 | 104 |
| 3500 | 106 |
| 4000 | 109 |
| 4500 | 111 |
| 5000 | 110 |
| 5500 | 106 |
| 6000 | 105 |
| 6500 | 106 |
| 7000 | 110 |
| 7500 | 113 |
| 8000 | 115 |
| 8500 | 115 |
| 9000 | 116 |
| 9500 | 118 |
| 10000 | 119 |
| 10500 | 116 |
| 11000 | 116 |
| 11500 | 121 |
| 12000 | 123 |
| 12500 | 117 |
| 13000 | 116 |
| 13500 | 116 |
| 14000 | 117 |
| 14500 | 120 |
| 15000 | 124 |
| 15500 | 123 |
| 16000 | 123 |
| 16500 | 123 |
| 17000 | 123 |
| 17500 | 125 |
| 18000 | 126 |
| 18500 | 127 |
| 19000 | 127 – Vehicle decent initiated |
| 19230 | 128 – “Communication Lost” at 43m AGL |
Conclusion
The Control and Telemetry Range test successfully concluded that the drone can be controlled by the ground control station from a distance of 19.23 km (11.95 miles). This is where we ran out of space to test longer distances. While it’s unfortunate that the low water condition of the lake prevented the full 20km test by a small margin, the performance past 19km was still impressive.
It is worth noting that the curvature of the earth did play more into the test than expected. Users should consider this when flying beyond visual line of sight (BVLOS) in flat terrain and aim to ensure the landing site or the pilot has some elevation difference.