Note：Because the 915MZH frequency band will conflict in many countries, the distance will be short or the conflict will be short, so it is best to choose 433MZH.

Very small size, light weight.
433Mhz frequency band. /  915Mhz frequency band
Transparent serial link.
Range of approx 1 mile with supplied aerial.
Demonstrated range of several kilometers with a small omni aerial.
Can be used with a bi-directional amplifier for even more range.
MAVLink protocol framing and status reporting.
Frequency hopping spread spectrum (FHSS).
Adaptive time division multiplexing (TDM).

Descriptions:
Support for LBT and AFA.
Configurable duty cycle.
Built in error correcting code (can correct up to 25% data bit errors).
Open source firmware.
AT commands for radio configuration.
RT commands for remote radio configuration.
Adaptive flow control when used with APM.
Based on the HopeRF HM-TRP radio module, featuring an SiLabs Si1000 RF microcontroller.
3DR Radio Telemetry Kit 433Mhz Module Open source for APM 2.5 2.6 2.8.
The 3DR Radio is the ideal way to setup a telemetry connection between your APM and a ground station.
Small, inexpensive and with great range, the 3DR radio uses an open source
firmware which allows us to do things that cannot be done with other radios.

Specifications:    
Item Name: 3DR Radio Telemetry Module
Band: 433MHz  915MHz
Receiver sensitivity: -117 dBm
Air data rates: up to 250kbps
Transmit power: up to 20dBm (100mW)
Antenna connectors: RP-SMA connector
Output Power: 100mW (20dBm), adjustable between 1-20dBm
Interface: Standard TTL UART
Connection status: LED indicators
FPV Radio telemetry air module size: 50  x 27 x 10mm
FPV Radio telemetry ground module size: 70 x 22 x 11mm
Package size: 165 x 80 x 11mm
Color: Black