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).
PX4 does not support connecting an LTE USB module to the flight controller (and sending MAVLink traffic via the Internet). You can however connect an LTE module to a companion computer and use it to route MAVLink traffic from the flight controller. For more information see: Companion Computer Peripherals > Data Telephony.