This D4R-II is a full featured mini sized 4 channel receiver by FrSky.
What makes this receiver different the the D4FR? The D4R-II's data port allows you to connect a sensor hub so you can connect GPS, Variometer, temperature, RPM and all of the other great FrSky sensors. It also has 2 full length detachable antennas. All of this is available in a package just a little larger then the D4FR.
2 full length antennas (replaceable)
One external analog telemetry port and one digital data-stream port (connect to Sensor Hub FSH-01)
RSSI (PWM) and CPPM output - If CH3 and CH4 are connected by a jumper, CH1 will output RSSI (PWM), and CH2 will output CPPM for CH1~CH8
Lighter weight and physically smaller than D8R-II Plus & D6FR
Alarm warning on low voltage, poor reception, etc.
Instruction Manual for D4R-II
Firmware Upgrade Instructions