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jD-RF900 provides compact and yet powerful data communication. The key features are:

● No configuration required for out of the box RF communications
● Operating frequency range of 902 - 928Mhz
● Outdoor RF line-of-sight range of 40 km or more depending on the antennas
● Air data rate speeds up to 250kbps
● Diversity antenna support
● Operating temperature of -40 to +85 degrees Celsius.

Compliance and Worldwide Acceptances:

jD-RF900 sets is designed to be compliant to AS4268:2012, and FCC 15.247


Supported RF Data Rates 4, 64, 125*, 250 and 500 kbps
Indoor range 500m - 1km
Line-Of-Sight range 40km or more depending on antennas
Transmit power 0 to 30dBm in 1dBm steps
Receiver Sensitivity >121dBm at low data rates, >TBA at high data rates
Low Noice Amplifier >20dBm
Serial Data Interface +3.3v nominal, 3.3V tolerant
Configuration method AT Commands, APM Planner, Customised Configuration Tool
Frequency Band 902MHz - 928MHz
Interference Immunity FHSS (Frequency Hopping Spread Spectrum)
Serial Interface Data Rate 2400, 4800, 9600, 19200, 38400, 57600, 115200, 460kbps
Antenna Options Yagi, ½ Wave Dipole, ¼ Wave Monopole Antenna
Compliance Standards FCC Part 15.247, AS/NZS 4268:2012
Networking and Security
Addressing Options Network ID: 0 –255
Channels Up to 50 Frequency Hopping Channels
Supported Network Topologies Point to point, Multipoint1, and asynchronous non-hopping mesh1

1 Only available in firmware version 2.x and later

Power Requirements
Supply Voltage +5V nominal (+5V min, +5.5V Max, +6V ABS Max),
Transmit Current ~1 A peak at max power
Receive Current ~60mA



The software solution (see Useful Links) is an open source development which is also compatible with jD-RF900 Modem Tools (see Useful Links) and the 3DR Radio Config (see Useful Links) from 3D Robotics. It is called “SiK” and was created by Mike Smith and improved on by Andrew Tridgell and RFDesign.

A boot loader and interface is available using jD-RF900 Modem Tools and field upgrade of the modem firmware via the serial port.

The jD-RF900 Radio Modem is compatible with many configuration methods like the AT Commands and APM Planner. The AT Commands can be used to change parameters such as power levels, air data rates, serial speeds etc.

Integrated support for configuring the jD-RF900 Radio Modem is supported by the APM Planner, with other GCS solutions in development. Its default serial port settings are as follows:

● 57600 baud rate
● No parity
● 8 data bits
● 1 stop bit

The jD-RF900 Radio Modem has many software features which include:

● Frequency Hopping Spread Spectrum
● Transparent Serial Link
● Configuration by simple AT commands for local radio, RT Commands for remote radio
● User configurable serial data rates and air data rates
● Error correction routines, Mavlink protocol framing (user selectable)
● Mavlink radio status reporting (Local RSSI, Remote RSSI, Local Noise, Remote Noise)
● Automatic antenna diversity switching on a packet basis in realtime
● Automatic duty cycle throttling based on radio temperature in order to avoid overheating
● PPM (R/C signal) pass through (Control vehicle across radio).


5.1 Diversity

The jD-RF900x has two antenna ports and firmware which supports diversity operation of antennas. During the receive sequence the modem will check both antennas and select the antenna with the best receive signal. In the case of only one antenna connected, it will automatically select the port with the antenna connected. Testing by Silicon Labs has shown that link budgets can be improved in the order of 8dB by employing a diversity scheme.

● Spatial Diversity

Spatial diversity is the case where the antennas are separated by some distance from one another. It is recommended that two antennas connected to the RDF900 modem be separated by at least 25cm, more if possible

● Polarisation Diversity

Polarisation diversity is the case where the antennas are perpendicular to each other. i.e. one vertical, and one horizontal. . This is effective in reducing multipath effects which affect one or the other polarisation. This scheme also helps to maintain the link between non-static objects such as aircraft performing acrobatics by increasing the likelihood that one antenna will maintain the same polarisation as an antenna on the other side of the link.

5.2 Types of Antennas

Below are some examples of the antennas that can be used with jD-RF900 modems

● Yagi Antenna

Yagi antennas are recommended for Ground-Station applications due to their size. They have approximately 6dBi gain and give significant link budget improvement when compared to standard dipole, or monopole antennas.

● Quarter Wave Monopole Antenna

Quarter Wave Monopole Antennas are recommended for air-borne, or space constrained applications. They are required to be mounted on a ground plane of approx 20cm diameter or more to operate as intended. Using an RF extension cable with an RPSMA bulkhead connector will give good mounting options.

● Half Wave Dipole Antenna

The half wave Dipole antenna has approx 3dBi gain with an omnidirectional radiation pattern. It is suited for ground station, or large airborne applications.


RFD900x support firmware for simple pair (peer to peer), asynchronous mesh network and multipoint network. Available for download from the website (see “Useful Links”).

6.1 Simple pair (P2P)

The out-of-the-box firmware of the RFD900x radio modem is set to work in simple pair mode. If you purchased a bundle, you are only required to connect the antennas and supply to initiate the link. As soon as the pair synchronises, the on-board LED will become solid green.

6.2 Asynchronous non-hopping mesh

The asynchronous non-forwarding mesh firmware offers a straight forward communication option that allows the user to quickly transmit and receive data across a great distance between two or more nodes. If all the nodes are within range and have compatible parameters, communication between them will succeed.

It is also possible to establish forwarding between nodes in the network. (See the asynchronous firmware datasheet for details)

6.3 Multipoint synchronised mesh

The network requires that one of the devices assumes a base role to control the timeslot distribution of the surrounding radios. If one the nodes is out of the base’s range, communication is still possible if the parameter SyncAny is properly set.


The jD-RF900 modem can support the Hayes ‘AT’ modem command set for configuration. The AT command mode can be entered by using the ‘+++’ sequence. When doing this, you have to wait for 1 second before and after entering the command mode in order to prevent data being interpreted as data. When you are successfully in the AT command mode, an ‘OK’ prompt will be displayed on the screen and the jD-RF900 modem will stop displaying information from the other modem. Whilst in AT mode, you can use the AT commands to control the local jD-RF900 modem or the RT commands to control the remote modem.

To set certain registers to a particular value, follow these steps:

1. Use the command ATSn=X where n is the register number and X is the actual value. 2. Use the command AT&W to write the new values to the jD-RF900 modem. 3. Use the command ATZ to reboot the jD-RF900 modem. Figure 8.1 shows a table that gives a list of AT commands and their description

Table below lists AT commands and their description

AT Command Description
ATI Shows the radio version
ATI2 Shows the board type
ATI3 Shows board frequency
ATI4 Shows board version
ATI5 Shows all user settable EEPROM parameters
ATI6 Displays TDM timing report
ATI7 Displays RSSI signal report
ATO Exits AT command mode
ATSn? Displays radio parameter number ‘n’
ATSn=X Sets radio parameter number ‘n’ to ‘X’
ATZ Reboots the radio
AT&W Writes current parameters to EEPROM
AT&F Resets all parameters to factory defaults
AT&T=RSSI Enables RSSI debugging report
AT&T=TDM Enables TDM debugging report
AT&T Disables debugging report

Remote commands table that gives a list of RT commands and their description. The x parameter is optional where x is the node ID. For example: use RTI,1 to get RTI value for node 1 or simply use RTI to get the RTI value for the node set in the local NODEDESTINATION

Table for Remote modem commands

AT Command Description
RTI[,x] Shows the radio version
RTI2[,x] Shows the board type
RTI3[,x] Shows board frequency
RTI4[,x] Shows board version
RTI5[,x] Shows all user settable EEPROM parameters
RTI6[,x] Displays TDM timing report
RTI7[,x] Displays RSSI signal report
RTO[,x] Exits AT command mode
RTSn?[,x] Displays radio parameter number ‘n’
RTSn=X[,x] Sets radio parameter number ‘n’ to ‘X’
RTZ[,x] Reboots the radio
RT&W[,x] Writes current parameters to EEPROM
RT&F[,x] Resets all parameters to factory defaults
RT&T=RSSI[,x] Enables RSSI debugging report
RT&T=TDM[,x] Enables TDM debugging report
RT&T[,x] Disables debugging report


An air speed of 64kps will give a range of about 40km depending on antenna. If the air speed is set to be lower, the range of the wireless link increases but the amount of data that you can send will be limited. Therefore one has to compromise between range and data rate. The data rates that you can choose are only limited to 2, 4, 8, 16, 19, 24, 32, 48, 64, 96, 128, 192 and 250.

The air data rate is chosen depending on:

● the range that you need
● the data rate that you will be sending
● whether you send data in one direction or both
● whether you have enabled ECC or not
● whether you have APM firmware with adaptive flow control


9.1 How many antennas do I need to use?

One is the minimum. Two is recommended.

9.2 How do I connect the FTDI cable to the modem?

The black cable of the FTDI (pin 1) should connect to pin 1 on the modem.

9.3 What do I need to upload the firmware or to change the modem configuration?

Download the latest firmware (see “Useful Links”). Download the RFD900x Modem Tools (see “Useful Links”). Connect the FTDI cable to the modem and to a computer. Use the RFD900x Modem Tools to upload the latest firmware or to change the modem configuration (see “RFD900x Modem Tools User Manual”).

9.4 I upgraded to asynchronous firmware and the modems don't connect anymore?

The default setting for a modem is to have a NODEID set to 1 and DESTID set to 2. As communication is addressed NODEID must be different for all units and DESTID will set the modems to connect to.

9.5 How do I configure 2 base stations and one Airborne platform with 3 modems? (Asynchronous)

Set the Airborne platform as follows:

DESTID = 65535, (32768 from version 2.45F)

Set the ground station as follows:

NODEID = 2 or 3

This will allow the airborne modem to handover to multiple ground stations as it flies from the coverage area of one ground station, to another. Both ground stations can be connected and can control the Airborne platform simultaneously. (APM Planner using MAVLink)

RFD900x Firmware
RFD SiK firmware is standard SiK (open source)
RFD Asynchronous firmware
RFD Multipoint firmware

RFD900x Flash Programmer

FTDI Cable documentation

com/jdrf900x.txt · Last modified: 2019/05/08 07:31 by metro