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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When you say checked the baud rate to be 57600, did you check the settings on the individual radios? Use RFD’s tool for that, downloadable from their website. I remember I needed to use version 1.5 for some reason later ones didn’t wok for the 900+. Also, plug into the Pixhawk with a USB and confirm the baud rate on the auto pilot is set to 57600. It likely your radio is set to one thing and the Pixhawk is something else. I think the setting is SERIAL_1_BAUD or something

Can the rfd900+ take an sbus signal and send it to an rfd900u, which will then output that same sbus signal? 


I am also curious about powering the RFD900 externally or from the flight controller. It would be simpler to power the radio from the flight controller, so this is my preferred solution. Is it not recommended to do so because you risk to damage your flight controller by drawing too much current, or because the telemetry range could suffer because the radio cannot get enough power? Other outcomes? If it is a question of the range being restricted, I guess it is a matter of testing to see if the actual range you achieve is sufficient for your use?

Thanks for sharing any insight on this

I'm looking to put the antennas for my 900+ (for uav basestation) and 900x (for remote instrument control) up on a pole (up to 60' if possible).  Can I use SMA extensions to connect the RFD radios on the ground to their dipole antennas on top of the pole?  How far can antennas be extended without interfering with performance?  Is there a better way to do this?

Hi Thomas,

I'd think you would want to mount the modem on top of the pole and run data & power over the 60 feet (using a $30 active USB extension) rather than the coax because losses can be quite high.  Try this calculator - http://www.qsl.net/co8tw/Coax_Calculator.htm   It shows 9.2dB loss even with a 1:1 SWR with RG-58.  Of course, you could look into low-loss coax but I'm guessing that may get pretty pricey for 60 feet. Not sure.  Interesting project. Good luck.

Thanks for the suggestions.  I think I'll try to find someone who can make an active USB extension out of silicone wire or something so it's not going to break in sub zero temperatures.  I suppose this should also have some kind of shielding to?

Thomas, I think you may want to look at a TTL-RS485 converter. RS-485 is good industrial standard for long range wired communications, longer range and better immunity to noise than USB at long range. Silicone is not very good neither at very cold conditions. You may try PTFE coated wires, I use it for my high altitude projects where temperature is as low as -70 deg C.

Well, USB needs one twisted pair for each direction.  If you can't find an off-the-shelf outdoor type, maybe you could buy the indoor type and just use the electronics by replacing the cable with two silicone twisted pairs.  I do see an indoor one (SKU #1501-SF-52  at  sfcable.com).  The active electronics module is only on one end and it looks like that would be the end that plugs into your pc so it would be indoors (I assume) and wouldn't need to be outside where it might need to be heated.  Well lots of stuff to think about and experiment with. Sounds like fun.

If you were really going to go the home-made USB cable route, CAT-5e would be a good choice.  Here's some rated to -40C. Not sure about price but probably fairly cheap: 


Alright, I'm back. I've decided to use two RFD radio sets. Radio 1 is on the UAV and communicates with Radio 2. Radio 2 is in the Relay box mounted on a mast some distance from the Pilot. It is connected to Radio 3 using the Tx/Rx wires (Tx to Rx and vice versa). Radio 3 then communicates with the basestation. I'm having a really hard time getting the connection to be stable. Sometimes the basestation connects to the UAV at the same speed and ability as if there was no relay (once out of 20), but usually it connects in super slow mode where it is barely operating. Sometimes when I cycle the power on the relay, one of the radios starts in boot mode (solid red LED). It's so random and uncontrollable. Anybody have experience like this?

I've seen this with RFD900x using it to send data from an instrument to a computer. Each time it boots we have to cycle the power of the radio 1 to 5 times before we get a solid connection.
Isn't it always after you ask the question that the answer presents itself. We've figured out that the radio can't handle a constant stream of data when it boots up. If we wait to plug in the data wire until moments after booting up, everything is fine. It's the radio in the relay that's transmitting to the basestation that's giving us problems. The UAV is constantly chattering so it's as if it can't handle the noise when it wakes up in the morning. How would you set up this circuit so this problem isn't encountered? I can only think to have a switch that you turn on after the battery is plugged in.

HI Guys, 

Maybe my question has answer within the 60 pages, but I was not able to read them all. I hope you will be able to help me.

I would like to know if we need to fly 60km using the RFD900x, will it be possible? it is a fixed wings plane

We will use diversity antennas on the UAV and Yagi 14 dbi on the ground. The altitude of the plane will be 300m.

The Ground station will be at 3 meters height. 

We will put the radio in the wing. 

Also we saw those antennas from VAS: which one is better for our solution?

VAS 900 MHz BAZOOKA DIPOLE : https://www.readymaderc.com/products/details/vas-900-mhz-bazooka-di...

and VAS 900 MHz TELEMETRY DIPOLE https://www.readymaderc.com/products/details/vas-900-mhz-telemetry-...

and VAS 900 MHz BAZOOKA DIPOLE https://www.readymaderc.com/products/details/vas-900-mhz-bazooka-di...

and VAS - 900 MHz Vee Antenna https://www.readymaderc.com/products/details/vas-900-mhz-vee-antenna



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