RFD900, RFD900+ - New long range radio modem

Hi All,

I would like to introduce you to a new radio modem that we developed for very long range datalinks!


Some of the key features of the RFD900 are as follows:

  • Multi point and point to point link capability.
  • 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.
  • RX SAW filter.
  • Passive front end band pass filter.
  • Open source firmware / tools, field upgradeable, easy to configure.
  • Small (30 x 57 x 13 mm), light weight (14.5g).
  • Compatible with 3DR / Hope-RF radio modules.
  • License free use in Australia, Canada, USA, NZ.


These modems are designed to support long range applications, while being easy to use and affordable.  

These modems have been flying in various platforms and have demonstrated excellent performance in real applications. 

RFD900 modems are now available at: http://store.rfdesign.com.au

Support within APM planner and the radio configurator from Michael Oborne is already available.

It works seamlessly with APM planner, all radio Mavlink parameters are available.

Update, December 2014:  The RFD900+ with improved specifications is available now at:


Seppo Saario



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Dear all,

I have two questions regarding the ¼ wave length monopole antenna that comes with the RFD868+ and ground plane. Thankful for any comments!

 - The antenna:


1) The antenna needs accoring to the description a ground plane for optimal performance, but how do you usually mount the GND plane when the connector is 90 degree turned?

2) We intend to use the RFD868+ radio modem on a flying wing for long range telemetry and I am considering different antenna options. My question is, if I place the monopole antenna facing downwards and add a ground plane, then I will gain in antenna performance (compared to no GND plane) but this will also restrict the radiation to the lower part of a sphere centered at the airplane. So as soon as I am in a rolling motion turning towards me I will have zero connection since the ground plane is between the transmitter and receiver. Is this something any of you have experienced and if so how do you usually mount the antenna and the ground plane to avoid it?


Hi Carl,
I've never added a special ground plane. The cable shield acts as one half of the antenna so that, although it's called a monopole, it's really a dipole. If the antenna and cable are mounted so that they are in-line, the radiation pattern will be fairly omni-directional. But for your antenna, the cable is probably at a 90 degree angle to the antenna which is going to have a lopsided pattern that's stronger in some directions than others. I've always used tranceivers that have two diversity antennas like the RFDs and mounted them at 90 degrees to each other with one vertical and one aligned horizontally along a wing. This has given very good reception regardless of the plane's orientation to the ground station. If you do add a ground plane, then I would think it would be best to mount two of those antennas at 180 degrees from each other, on opposite sides of the ground plane. But I don't know why go to all the trouble (plus add the extra weight) when there are easier ways to do it.

Got mine already wired in to a 3DR Pixhawk, but connecting to the usb cable to Laptop on Base station it connects at Com Port 6 57600 but I get a error message saying;

"Failed to load Command Mode"   

And the Led on the 900+ stays Solid Red.

What's happening ??

Hi Dan,

Thank you for the comments. I will start without ground plane and see if I can improve the performance later after some range tests.

Dear all,


I have a connection problem with my RFD868+ modems and I am looking for some input on how to solve the issue.


- If I connect two RFD868+ to my computer via FTDI cables the connection is solid between the two.

- If I instead connect one of them to a Pixhawk (on TELEM1 connector) and monitors the connection in QGC the connection is lost every 3rd or 4th second.

- The connection drop is very regular, but the connection is regained after approx. 2 seconds.

- It does not matter if I power the pixhawk via USB or 5V BEC.

- It does not matter if I power the radio modem directly from the Pixhawk or from 5V BEC.

- It does not matter if I replace both the RFD868+ modems with a second pair.

- If does not matter if I lower the amount of data transmitted from the Pixhawk.

- If I instead replace the radio modems with 3DR 433 MHz modems the connection is solid without any drops.

The configuration of the RFD868+



















The configuration of the 3DR 433 MHz modems


















I would really appreciate all help.

Best Regards

I am trying to find the source of the connection issues, do someone know the answer to the questions listed below or where I can find them?

1) Sometimes when I power up the modems the green led is completely off and the red is constant on. I think this means firmware update mode, why is this happening?

2) When the connection is lost the green led on the modems start to flicker, is this "normal" behavior for packet loss or is it an indication of something else?

3) According to the manual you may use the modem with one antenna. Do I need to terminate the second antenna connector with a 50 Ohm impedence or just leave it open?

Thank you very much,


1) If the Red led stays on you will have to update the firmware, goto RFDesign.com and Download;


RFDsik-v1.12-RFD900p.ihx  (Latest Firmware)

Install the RFDtools and put the RFDsik-RFD900p.ihx in the same folder/directory, and run the RFDtools and install the Firmware from the RFDtools.

2) the green led  On it is connected between the Base and Plane modems.

3) the modems will work with one antenna and you do not need to terminate the other antenna connection, but it is best to use both antenna's

You'll have to connect each Modem to the usb cable to Laptop to update Firmware, most likely the old firmware will be 1.9 version.

At the bottom of the RFDtools there are three boxes that needs to be checked,




If you are connecting to Pixhawk.

I could not get the mavlink to connect using MissionPlanner, I had to install APMplanner .

Hi All, 

Has any body tested the new RFD868+ ?

This may be a stupid question but will the 1w 868MHz have the same range as the RFD900+ (1w)? 

Will the 900MHz GSM band interfere with the RFD900+ or vise versa?



Hi All,

I recently purchased the Event38 RFD900 telemetry radio bundle to compensate for the limited range of my existing 3DR 915MHz telemetry radios.

I was under the impression that the RFD900 radio is compatible with the 3DR 915MHz telemetry radios if the parameters are set to the same values and the same check boxes checked. I have a friend who's RFD900 radios does communicate with his 3DR telemetry radios. 

Unfortunately I found out that that is not necessarily true in all cases.

I tried using one of the RFD900 radios to connect to the 3DR 915MHz radio on my rover and could not make a connection.

Both radios had their green leds on and I could see both radio's red leds flicker.

Both the RFD900 and the 3DR radios are running firmware version 1.9.

I plugged each telemetry radio into my laptop and used MP to verify that the parameter settings and check boxes were identical to each other except for one parameter called "format".

The RFD900 radio's format parameter value was found to be 26 while the 3DR radio's format parameter was found to be 25.

It appears that a RFD900 radio with a format parameter value different from the 3DR radio's format value will not communicate with each other.

I then verified that the two RFD900 radios would communicate with each other since they both had the same format parameter value of 26.

The format parameter is not adjustable in the Mission Planner's telemetry radio screen and neither in the 3DR telemetry radio configuration application. 

Is the format parameter only adjustable at the factory or can I use the RFD900 Modem Tool to adjust the format parameter value or will updating the existing RFD900 firmware resolve the issue?

Though I suspect that the format parameter value is factory set and not adjustable.

Comments please!




Thank you for the answer. However, unfortunately I have still not been able to make any of my RFD868+ modems to work and would be happy for any further input. Is anyone using the RFD868+ successfully?

I checked the firmware on my modems and they are SiK 1.13 (which is newer than the one that may be downloaded from the RFDesign website)


Today I tried two 3DR radios and connected them both to my computer. The green led is solid green on both of them and the communication works perfectly. (I had two cutecom consoles open and were sending messages back and forth with no problem)


But if I instead connect two RFD868+ modems the same way the connection is constantly dropped every now and then. I set up the modems the same way as the 3DR radios as follows:



















I would really appreciate any help




Hi Carl,
I had something similar with the RFD900s. It turned out to be the voltage drop during each transmit burst. I had to add a 100uF cap right at the modem because the supply wires were a little small for the distance I ran them. Have you tried setting the power to minimum to see if it has any effect? It's just a thought anyway.

where exactly did you have to install the capacitor at? which cable and how?   thanks

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