Radiomaster ER3 PRO PWM Dual-Band Gemini/Gemini-X

RadioMaster ER3 PRO PWM Dual-Band Gemini/Gemini-X is a compact dual-band PWM receiver with full diversity for the ExpressLRS system on 2.4GHz and 868 MHz frequencies, suitable for RC airplanes, gliders, and other models with servos controlled directly from the receiver, especially where space inside the fuselage is limited. The receiver offers 3 PWM channels plus a CRSF/SBUS serial output, allowing connection to a flight controller or stabilizer.

It is based on two Semtech LR1121 RF chips, each capable of operating on 2.4GHz and in the sub-1GHz band. The receiver features full diversity (“true diversity”) — two antenna inputs and two RF chips. It supports both Gemini and Gemini-X modes: in Gemini-X mode, one band is assigned to each antenna input (ANT1 receives on 868 MHz, ANT2 on 2.4GHz), allowing the use of antennas tuned precisely for the respective band or high-gain directional antennas, providing greater link margin. The combination of two bands increases connection reliability in various environments. Telemetry output is up to 100mW (adjustable via LUA script). The receiver is compatible with all ExpressLRS transmitters and modules, including radios with integrated ELRS.

Antennas connect via durable MMCX connectors, which provide a secure connection and allow easy replacement. The package includes two 25cm antennas for 2.4GHz and two 25cm dual-band antennas, allowing a set to be selected according to the mode used. Antennas should be positioned perpendicular to each other and away from metal and carbon parts of the model. The receiver operates from 5-12V, typically supplied by an ESC BEC. It independently measures two voltages through separate ADC channels: receiver supply voltage (V-PWM, up to 12V) and flight battery voltage through the EXT-V input with a JST-GH connector in the 4-70V range. The external UART port is used for telemetry, external devices, and ERS sensors. The UART and EXT-V ports use locking connectors to prevent accidental disconnection due to vibrations. Settings and firmware updates are performed via Wi-Fi and WebUI without removing the receiver from the model. The electronics are protected by an injection-molded case with flat sides for easy mounting, measuring 49.2x26.8x13mm. The receiver weighs 13.5 grams without antennas.

Important warning: Voltage at the EXT-V input must not exceed 70V, otherwise the receiver will be damaged.