# Telemetry Radios/Modems
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
- Microhard Serial Telemetry Radio
- CUAV Serial Telemetry Radio
- XBee Serial Telemetry Radio
- HolyBro XBP9X Telemetry Radio (Discontinued)
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.
# Allowed Frequency Bands
Radio bands allowed for use with drones differ between continents, regions, countries, and even states. You should select a telemetry radio that uses a frequency range that is allowed in the areas where you plan on using the drone.
Low power SiK radios, such as the Holybro Telemetry Radio, are often available in 915 MHz and 433 MHz variants. While you should check applicable laws in your country/state, broadly speaking 915 MHz can be used in the US, while 433 MHz can be used in EU, Africa, Oceania, and most of Asia.