Telemetry Radios can (optionally) be used to provide a wireless MAVLink connection between a ground control station like QGroundControl and a vehicle running PX4. This makes it possible to tune parameters while a vehicle is in flight, inspect telemetry in real-time, change a mission on the fly, etc.
PX4 supports a number of types of telemetry radios:
- SiK Radio based firmware (more generally, any radio with a UART interface should work).
- Telemetry Wifi
PX4 is protocol compatible with SiK Radio and will generally work out of the box (though you may need to change/use an appropriate connector).
WiFi telemetry typically has shorter range, higher data rates, and makes it easier to support FPV/video feeds. One benefit of WiFi radios is that you only need to purchase a single radio unit for your vehicle (assuming the ground station already has WiFi).