I use two of these on Pixhack V3’s in helicopters.
Set channel 12 output on the DragonLink receiver to SBus (12 channels) and connect it to the Pixhack’s RC IN.
You need to make up a telemetry cable and hook it from the Pixhack’s telemetry port to the UEXP port 1 on the V3 large receiver. There is specific settings you must set the port to in ArduPIlot, as well as the SR (Stream Rate) settings for the telemetry. This is in the DragonLink documentation. It will not work unless you set those correctly.
You’ll have to pay attention to getting the Tx/Rx right from the Pixhack’s telemetry port to the UEXP port on the large DragonLink receiver or it won’t work. Rx on the receiver goes to the Tx pin on the Pixhack. Tx on the receiver goes to the Rx pin on the Pixhack.
On the transmitter side DragonLink is not officially supported with the Horus. You may get it to work by following the documentation for the Taranis X9D Plus. I could not get it to work with the Horus. But it works fine with the X9D Plus Taranis. Set your UEXP output to FrSky SPort on the DL transmitter. Set your USB output to radio modem. Make sure the rest of the settings in DL transmitter are correct before you switch the USB because you will not be able to connect to the transmitter with the DL software anymore after you change your USB configuration on the transmitter. The output of the UEXP port goes into the Taranis serial port. There is four pins - power, ground, SBus and telemetry. You hook your ground station with QGroundControl to the USB cable for MavLink telemetry on the ground station. You have to write a custom Lua Script to display the telemetry from the aircraft that is converted to FrSky Sport on the Taranis. Or set up one or two custom telemetry screens. You will have GPS, heading, altitude, speed, rate of climb, voltage, current, and a bunch of other stuff on the Taranis (use Discover New Sensors).
I don’t use the bluetooth on the DL transmitter because I found it to be extremely unreliable. The USB connection to the ground station never fails.