I have a RFD900a and a RFD900+. Are they compatible with each other?

Yes! Though the firmware is different if you upload similar versions to each of the modems they will connect to each other.

I have a RFD900x and one of the earlier types “900a”,”900+”, 900u”. Are they compatible with each other?

No, sorry. The 900x has a much faster processor, more ram, and more features (such as ppm pass-through), so the firmware on this generation radio is very different to earlier generation radios ( it’s a re-write!).  We’ve tried our best to make it user-configurable just the same way as the old radios ( the AT commands, but  they will NOT connect to each other.

I’m using a Pixhawk/APM and it’s not working!

Ensure the device is getting power, when using any of the RFD900 series radios at higher power levels you may require to supply power separately most devices are unable to provide the inrush of current needed when transmitting. This can easily be tested by reducing the power level in the range of 10-15. If this works change your wiring to provide power to the modem as well as your flight board.

I have programmed the modem and now it’s stopped working!

Ensure you are using the correct firmware, there are 4 types of modems 900a, 900+ , 900u and 900x. 900u are our smallest unit presently, 900a have a blue circuit board, 900+ and 900x have a black circuit board. For the 900u and 900+ you will require to use the RFDTools 1.5 or above due to the new programming protocol for these devices. If you have programmed the wrong firmware you might have to force the device into bootloader mode (see the bottom of the products page for more details)

I have a programmer. Can I change the bootloader?

It’s not recommended to change the bootloader on the modems, we run each modem through calibration before we send it out. Programming the device via the SiLabs USB debug adapter will wipe this calibration data.

How many antennas do I need for proper operation of the RFD900?

One is recommended, though two will give you better performance if mounted externally away from each other. The modems use diversity switch to determine the strongest antenna port and will receive and transmit on the strongest signal at the given time.

Though it’s not recommended to run these devices without any antennas connected, having no antennas connected will not damage the device in any way.

I have problem when connect RFD to laptop using the supplied FTDI cable

Lets test the FTDI Cable to see if this is working first:

  • Disconnect the modem from the FTDI cable and the computer
  • Connect the Orange and Yellow wires together on the FTDI cable, you have now created a loopback on the RX/TX lines
  • Plug the cable back into the computer
  • Open a console port (my favourite is CoolTerm)
  • With a connection open, type something, you should see what you type.
  • Remove the link, type something again. Nothing should appear

If this procedure above doesn’t work as expected, the FTDI drivers or the FTDI cable isn’t working. Please try reinstalling the drivers (see http://www.ftdichip.com/Drivers/VCP.htm)

Can I send video through the link?

No, sorry. The RFD900a/+/u modems are unable to carry video down the link due to the high bandwidth requirements.

The modems aren’t connecting! What should I do?

Out of the box the modems come with software that will link 2 modems together. Having three or more on with the same Network ID will confuse them and cause undesirable effects. If you want to link more than 2 modems please read our MP SiK guide.

If you have a third modem handy with the same settings (Air Rate, Network ID) you should be able to find out quickly which modem has bad settings or is faulty. If not, try to reload the factory default settings onto each modem, this can be done via our Modem Tools. If the versions are the same and resetting the settings didn’t work contact us and we will try and help you further.

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 (see above)
Please Note the jumper between pins 4-6 to power the unit on
More information can be found on the RFD900 Product page

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

The easiest way is to get a copy of the RFDModem Tools and the latest firmware if needed. These can be found on the downloads page.


Whats the difference between SiK, RFD SiK and RFD MP SiK?

We have branched away from the main SiK tree and as such have renamed our releases RFD SiK to try differentiate between the main branch versions and ours. MP is the multipoint branch (see below for more information)

I have updated to RFD MP SiK version 2.x. Now nothing works!

MP SiK is our special build to allow you to connect more than one modem together in a network. This build requires each node to be configured before they will connect. More information on settings are coming soon.

I want to do some processing of the data, can I do this?

You can! Though be prepared to get your hands dirty. There are many ways but I would recommend getting a Arduino shield as this would be the easiest way forward and a quick proof of concept. If you really want to get your hands dirty you can checkout the code in our github and try to compile it, then start changing it to your hearts desire

I’m wanting a low latency link, how do I achieve this?

In the settings you can change the Air data rate up to 255 to get the maximum out of the link. By doing this you will lose range as to the data is easier to corrupt due to noise. The reverse is also true, the slower the Air data rate the further your link will stay connected.

I’m losing data over the link, what can I do?

One of the common causes of loss of data is trying to transmit too fast, this can be improved by increasing the Air data rate (as above) and/or turning on RTS/CTS if your hardware supports it.

When using MP SiK what would happen if the 10 nodes want to send data at the same time

The software is designed to give a slice of time to each node to transmit, if the node doesn’t have anything to say it will send a basic packet to the network informing everyone that it has nothing.

Another node then has the ability to negotiate and transmit a bit more of its payload.

As such the network does handle collisions but if two nodes are sending data back their data will be intertwined when received. Sometimes this isn’t desirable but there’s no way around the problem presently without making the sent data short and sweet to ensure it is transmitted in one transmission slot.