Quick Answer
To set up RFD900 radios with ArduPilot or PX4, wire the air unit to a TELEM port on your flight controller, match the Net ID and air data rate on both radios using RFD Tools, set the matching SERIAL parameters in your autopilot, then confirm the link in Mission Planner or QGroundControl.
Wiring the Air Unit
The RFD900 air unit connects to a serial port on your flight controller, usually one labeled TELEM1 or TELEM2 on a Pixhawk-style board. You need four wires: power, ground, transmit, and receive.
Double-check that transmit on the radio connects to receive on the flight controller, and receive on the radio connects to transmit on the flight controller. This crossed wiring trips up many first-time builders. Our Pixhawk cables guide explains connector types and pin order in more detail.
Confirm your radio's power draw matches what your chosen TELEM port and power source can supply, since some radio models draw more current than others.
Setting Up RFD Tools
RFD Tools is the configuration software for RFD900 radios. Connect your ground radio to a computer with a USB cable, then open RFD Tools to read the current settings.
Key settings to check and match between your air and ground radios:
- Net ID: a code that keeps your radios from linking to someone else's nearby radios.
- Air data rate: the speed the radios send data over the air. Lower rates usually reach further.
- Frequency band and channels: must match on both radios, and must be legal for your region.
Change these settings on the ground radio, save them, then repeat on the air radio so both match exactly. A mismatch on any of these settings will stop the link from connecting.
Matching Air Speed Settings
Air speed, in this context, refers to the radio's over-the-air data rate, not the drone's flight speed through the air. A higher air speed sends more telemetry data per second but usually reduces range. A lower air speed extends range at the cost of slower updates.
For most missions, a moderate air speed setting works well. Push it higher only if you need fast telemetry updates and you know your range needs are short. Push it lower if long range matters more than update speed.
Setting SERIAL Parameters in ArduPilot
Inside ArduPilot, using Mission Planner's full parameter list, set the SERIAL port connected to your radio to protocol 2, which is MAVLink 2. Match the baud rate parameter, usually SERIALx_BAUD, to the baud rate your radio uses, which is commonly 57600.
Save the parameters and reboot the flight controller. If you are new to ArduPilot setup overall, our ArduPilot setup guide covers the wider first-configuration process.
For PX4, the equivalent settings live in the parameter list under the matching TELEM port's baud rate and protocol settings. Confirm these in QGroundControl before testing the link.
Testing the Link
Power up the drone and the ground radio together, away from other radios that might interfere. In Mission Planner or QGroundControl, connect using the matching COM port and baud rate.
You should see telemetry data appear, including GPS status, battery voltage, and flight mode. If nothing connects, recheck your Net ID, air data rate, wiring, and SERIAL parameters in that order, since these are the most common failure points.
Test the link on the ground first, at a short distance, before trusting it for a real flight. A link that fails to connect at ten meters will not work better further away.
Checking Signal Quality Before You Fly
Once connected, most radios report a signal strength value in the ground station software. Watch this value as you walk away from the drone with the radio powered, to get a feel for how signal quality changes with distance and obstacles.
Note where the signal starts to weaken noticeably. That distance, with a safety margin subtracted, is a reasonable starting point for your first real long-range test flight. See our RFD modem comparison if you are deciding between different RFD radio models for your build.
Common Setup Mistakes
A few mistakes come up again and again with RFD900 setups. Knowing them ahead of time can save you a frustrating afternoon.
- Swapped transmit and receive wires. This is the single most common wiring error and stops the link from connecting at all.
- Different Net ID on each radio. Even one character different will keep the radios from finding each other.
- Wrong baud rate in ArduPilot or PX4. The SERIAL parameter must match the radio's configured air data rate, not just any common value.
- Antennas left disconnected during testing. Some radios can be damaged by transmitting with no antenna attached, so always connect antennas before powering on.
- Testing indoors only. Walls and metal objects can make a link look worse than it really is outdoors, so do a short outdoor test before judging performance.
Keeping a Working Configuration Backed Up
Once your RFD900 link is working reliably, save your settings. RFD Tools lets you export a configuration file you can keep alongside your other build notes.
If a radio ever needs to be replaced, or you reset one by accident, this saved file lets you restore a known-good setup in minutes instead of guessing at settings again. This habit matters even more if you run several drones with slightly different radio settings for each one.