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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        • Any electronic circuit that is working normal will have a 10% fudge factor of 5 v , so your circuit is showing that it is working normal. If you had a short it would be much less.

          The reason your voltage intially drop to 4.2v was the APM couldn't handle the load.

          You have what is known as a Load and no Load voltage drop when you connect the 900.

          The BEC will show a no Load voltage reading of 5.11

          When you connected the 900, you got Load voltage of 4.99v that is only a .2 tenths drop in voltage and that is within the 10% fudge factor.

          So to put it in simple terms your 900 is OKAY!!

          Is this a Base Station or a on board the Drone?

          The cable that came with the 900 is most likely wired correct.

          The cable that you have for on board the Drone to the 900 is a different thing , you said you have a APM

          I will upload a picture of the wiring for a Pixhawk to show you how the on board cable should be wired.

          The +5v and -Grd from the BEC goes to pins 2 an 4 the 900.

          You will see in the Picture a +5 and ground - from the Pixhawk, be sure that the -grd wire is connected to pin #1 on the cable going to the 900. Don't connect the +5v wire from the APM to 900 elimnate this wire, just tape it up. The BEC will be handling the powering of the 900. I have a Separate BEC powering the 900 on the Base Station and a separate BEC powering the 900 on the Drone, the APM cannot handle the +5 load to power the 900

          The reason for connecting the -grd wire only is to make sure that your feeding the 900 to a common ground with the rest of your Drone.

          If all the wiring is all correct at Drone and Base Station and you get a solid Red on the 900 check for a Firmware upgrade.

          The six pin cable on the Drone to 900 are different on other Flight Controllers.



          • ... Thankyou so much James for helping out with questions on the RFD900's - It is really appreciated !

          • Hi,
              I am understand you clearly and I tried your all wrote things but nothing change. Yes I don't connect red (+) cable. This broken rfd900 on a plane also I tried ground station on netbook.

            When I connect to ground station telemetry (healty one) from bec voltage is 5.11 like undoad voltage but if ı connect to broken telemetry (on plane one)  voltage is 4.99. I think it seems some problem but I dont now what is the problem.

            This monday I wil go to electronics repair shop. Maybe he understand whats the problem.

            This telemetry really amazing product.But 900 price expensive for me. $ is expensive in Turkey.

            I was fly 10.3 km  and the telemetry's rssi value is %65. Really good value.


            If I can't fix this problem maybe Seppo give some advice or help me. I belive :)

            • Your Quote;  When I connect to ground station telemetry (healty one) from bec voltage is 5.11 like undoad voltage but if ı connect to broken telemetry (on plane one)  voltage is 4.99. I think it seems some problem but I dont now what is the problem.

              4.99v is OKAY.

              Are you using separate BEC on (on Plane one) or are you having voltage from APM to power the 900 ?

              If so,  that tells me the APM can't handle the load and your going to have to use a separate BEC to power the 900 on Plane.

              Another thing Enes, when your trying to communicate to Plane from Base station, you are going to have to move the Plane at least 30 meters from Base Station.

              When you have two 900's close together,  they won't communicate with each other. 

              • ''Are you using separate BEC on (on Plane one) or are you having voltage from APM to power the 900 ?''

                Normally I'm using APM to power the 900. Now if I connect to broken telemetry to Apm only Apm power led (orange or yellow one) on. Ezuhf rx, gps etc. is not working. If I disconnet to broken telemetry to apm everything is ok.

                When you write seperate Bec (5v) i tried on apm and ground station. Yes I disconnect red (+) cable. Telemetry is not working. Yes when I powered seperate bec 5v to rfd900 apm, gps, ezuhf rx etc. all system is working but telemetry is not working.

                • Hi Enes,

                  Sorry to hear you are having some trouble!... - How did your visit to the repair shop go?, were they able to confirm the setup was OK?

                  Firstly, if a modem has a red-led by itself, the modem does need to be re-programmed.  This happens on a small % of units, which we have not found the issue behind yet.  Reprogramming the units fixes it and they remain OK.

                  You can download the latest modem tools, and latest firmware at the following link:


                  If a modem has a red-led it would need to be forced into bootloader mode manually, then upload firmware.  To do this you need to short pin 1 on the 9 way header to ground when you apply power.  It is next to the label "BOOT" on the 9 way row of pads.  Then, upload firmware using modem tools.  The RFD900+ modems need the "900p" version of firmware.

                  When the modems are normally working, you should see a blinking green LED for few seconds while it synchronises, then, solid green LED when it has connection between 2 modems.

                  You can also test if a modem is working correctly ( in terms of physical damage dragging rails etc) by swapping them between the ground and air side, as there is no difference between them.

                  It would be worth knowing if there is any difference between them when you swap them between air and ground station.  Let me know how things go.


                  Home | RFDesign Files
                  Here you will find Supporting files, Binaries and Tools to use our products
                  • Hi Seppo,

                    I go to repair shop yesterday. He examined rfd900. But he dont find the problem. He said maybe telemety's chip is burn. Because when we connect to power the telemetry, chip is little warming up. I order to a new chip from aliexpress. Si1002

                    Can we upload a firmware new chip?

                    Seppo I try force boot but nothing change. Computer can't see telemetry and ı can't upload new firmware.

          • I'm using a RFD 900 and an APM 2.5.  The RFD 900 is set at one watt and I have no problem with the APM powering it.  Just so you all know.


            David R. Boulanger

  • Hi Seppo,

    I sent this email to RF Design on 8/31.  Maybe you didn't get it, either?

    Hi RF Design,

    For several years, I’ve used your RFD 900s in my ground stations to communicate with either RFD 900s or 3DR radios on my aircraft.  I currently have 8 ground stations happily talking with aircraft using ECC.  I recently purchased six RFD 900+ radios and discovered they will not communicate with my RFD 900s or 3DRs when ECC is enabled.  They will only communicate with other RFD 900+ radios if ECC is enabled.

    When I use two 900+ radios with ECC enabled, both units have solid green LEDs and blinking reds when they communicate.  However, with a 900+ and a 900 (or 3dr), the 900+ has a solid green LED and constantly blinking red LED (handshaking?), but the remote 900 (or 3dr) is always blinking green.  The remote isn’t detecting the 900+, but the 900+ is detecting the remote.  If I disable ECC on both ends, they link and communicate.

    It is important to me that new ground stations that use RFD 900+ transceivers are backward compatible with my existing aircraft that use either RFD 900s or 3dr radios and that they work with ECC enabled.  I understand that it is your intention that the 900+ be fully compatible with both the 900 and 3dr radios, but right now that is not the case.   

    Please let me know if you have a firmware fix for this.

    Is this something you are working on?  The improvements to the 900+ modems aren't of much value to many of us if they won't work with our 3DR or 900 modems.  


    • Hi Don,

      There has been a bit of work back/forth over time with ECC.  The problem has been limited code space available on units with features that have been added.  http://files.rfdesign.com.au/firmware/

      Has the current and a few good historical versions.  RFD900p V1.9

      would be worth checking with compatibility with 3DR modems and older firmware.

      My experience with ECC has been that some times it has trouble loading parameters in mission planner, and the extra correction capability has not really been needed for most applications.  As a result, it hasn't had much of a focus over time.  In addition, ECC doubles the bandwidth requirements for the link, reducing the telemetry rates available.

      Modem firmware development has slowed a little, the next features needing to be tested are AES encryption..


      Firmware | RFDesign Files
      Here you will find Supporting files, Binaries and Tools to use our products
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