RFD900x Modem

RFD900x Radio Modem

RFD900 Radio Modem

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The RFD900x is a high performance 900MHz, ISM band radio modem covering the 902 – 928 MHz frequency band. It is designed for long range serial communications applications requiring best in class radio link performance.

New Features for the X series:

  • New Processor, ARM 32 bit core.
  • Air data rate: 500kbit/s.
  • AES Hardware accelerated encryption. *Fully working*
  • RC PPM Passthrough with telemetry at the same time.
  • GPIO Pin Mirroring – see datasheet for more.
  • Original SiK point to point firmware implemented.
  • Asynchronous multipoint firmware, *Beta release*

Key Features:

  • Long range >40km depending on antennas and GCS setup
  • 2 x RP-SMA RF connectors, diversity switched.
  • 1 Watt (+30dBm) transmit power.
  • Transmit low pass filter.
  • > 20dB Low noise amplifier, high IP3.
  • RX SAW filter.
  • Passive front end band pass filter.
  • Fully ESD protected + filtered – Every IO port is protected and filtered.
  • Re implemented SiK and Multipoint SiK firmware, field upgradeable, easy to configure.
  • Small, light weight.
  • License free use in Australia, Canada, USA, NZ.
  • Note: Not air-compatible with older “+” series modems with current software.


The RFD900 is designed to be compliant with the following standards:

  • FCC Part 15.247 (Frequency hopping and digitally modulated intentional radiators)
  • AS/NZS 4268:2012 (Radio equipment and systems – short range devices)


  • Frequency Range:  902 – 928 MHz (USA) / 915 – 928 MHz (Australia) / 868 – 870 (European Band)
  • Output Power: 1W (+30dBm), controllable in 1dB steps ( +/- 1dB @ <20dBm, +/- 0.5dB >=20dBm typical )
  • Air Data transfer rates: 4, 64, 128, 250, 500 kbit/sec ( 64k/128k default )
  • UART data transfer rates: 2400, 4800, 9600, 19200, 38400, 57600, 115200 baud , and higher. ( 57600/115200 default )
  • Receive Sensitivity: >121 dBm at low data rates, high data rates (TBA)
  • Size: 30 mm (wide) x 57 mm (long) x 12.8 mm (thick) – Including RF Shield, Heatsink and connector extremities
  • Weight: 14.5g
  • Mounting: 3 x M2.5 screws, 3 x header pin solder points
  • Power Supply: +5 V nominal, (+3.5 V min, +5.5 V max), ~800 mA peak at maximum power
  • Temp. Range: -40 to +85 deg C, tested operational from -73 to +123 deg C.


  • RF : 2 x RP-SMA antenna connectors – it is OK to have only one antenna connected
  • Serial: Logic level RS232 (+3.3v nominal, +5v tolerant)
  • Power: +5v, ~800mA max peak (at maximum transmit power)
  • GPIO: 6 General purpose IO (Digital, ADC, PWM capable).

The following cable from FTDI is compatible with the RFD900 modem. Pin 1 of the FTDI cable connects to Pin 1 of the RFD900 header.

To power the modem from the +5V USB power, a jumper is needed between pins 4 and 6.
To power the modem from an external +5V supply, connect power to pins 2 and 4.

9 way test pad pinout

9 way test pad pinout

Physical pinout on the RFD900

Physical pinout on the RFD900

Pin Signals and Layout

Pin # SiK Mapping Name 900a Name 900u Direction Description Max Voltage
1 GND GND Ground 0V
2 GND GND Ground 0V
3 CTS CTS Either Clear to send 5V
4 VCC VCC Power Supply 5V
5 Vusb Vusb Power Supply USB 5V
6 Vusb Vusb Power Supply USB 5V
7 RX RX Input UART Data In 5V
8 0 P2.3 P3.4 Either Digital I/O 5V
9 TX TX Output UART Data Out 5V
10 1 P2.2 P3.3 Either Digital I/O 5V
11 RTS RTS Either Request to send 5V
12 2 P2.1 P1.2 Either Digital I/O 5V
13 5 P0.1 P1.0 Either Digital I/O 5V
14 3 P2.0 P1.3 Either Digital I/O 5V
15 4 P2.6 P1.1 Either Digital I/O 5V
16 GND Black Ground 0V

In case there is need to force the modem into boot mode, short circuit pads 1 and 2 (labeled BOOT) on the 9 way test pads.