RFD900 Radio Configuration

Reference RFD-TR-001. How to configure the RFD900x (ground) and RFD900ux (airborne) telemetry radios.

Note

Your radios ship pre-provisioned as a matched, encrypted pair — NetID, band plan and an AES-128 encryption key are set at delivery, and both ends must match or the link will not come up (both LEDs flash green forever, never solid). Radio settings are part of the aircraft’s delivered configuration: change them only when an RFD release or support instruction calls for it — see Firmware & Software Updates. Encryption keys are customer-specific; contact support@rocketfastdrones.com to rotate yours.

Over-the-air (OTA) configuration — the standard method

PX4 does not provide a serial-passthrough shell, so routine configuration of the airborne radio is done over the air from the ground station:

1. Connect the ground RFD900 to your PC and establish a link with the aircraft.
2. Open QGroundControl → the Radio / SiK Radio configuration tab.
3. Click Load Settings — settings for both the Local (ground) and Remote (aircraft) radios load.
4. Modify the Remote settings as required (NetID, power, duty cycle) and Save — changes are sent over the air.

Danger

Never change the baud rate, encryption settings, or firmware over the air — the link breaks the moment the change applies, leaving the airborne radio unreachable in flight configuration. Those changes need the serial-passthrough method below, on the bench.

Deep changes — serial passthrough on the bench

Changing the airborne radio’s baud, encryption, or firmware requires a direct serial path. The RFD900ux has no exposed connector once installed — the path is through the autopilot, by temporarily flashing ArduPilot (which has a passthrough feature PX4 lacks):

Caution

Bench procedure — props off, aircraft restrained. Temporarily flashing ArduPilot is approved only for this procedure; return the aircraft to its RFD firmware and parameter file afterwards (per Firmware & Software Updates) and complete the acceptance check before flight.

1. Power: connect the flight battery (props off) — the airborne radio is powered from the servo-rail supply and stays dark on USB power alone.
2. Flash ArduPilot via QGC → Vehicle Setup → Firmware (select ArduPilot, your board).
3. Port order matters: open your serial terminal (e.g. CuteCom, 57600 baud, /dev/ttyACM0) before opening QGC, or QGC seizes the port.
4. In QGC set: SERIAL1_BAUD 57, SERIAL1_OPTIONS 1024 (stops MAVLink on the port), SERIAL_PASSTIMO -1 (bridge stays open), then SERIAL_PASS2 1. Wait ~30 s.
5. In the terminal, set line ending None, send +++ → the radio answers OK (AT mode). Then set line ending CR/LF for all further commands.
6. Configure (cheat sheet below), AT&W to save, ATZ to reboot.
7. Re-flash the RFD PX4 firmware + parameter file and run the acceptance check.

SiK AT-command cheat sheet

Diagnostics:

Command	Function
ATI	Firmware version
ATI5	Print all parameters (S-registers)
ATI7	Signal-strength (RSSI) statistics

Configuration (ATS<register>=<value>):

Command	Function	Notes
ATS1=57	Serial baud (57600)	Must match the autopilot’s telemetry-port baud
ATS2=64	Air data rate	Lower = more range, less throughput
ATS3=<0–499>	NetID	Both radios must match
ATS4=<1–30>	Transmit power (dBm)	30 = 1 W maximum
ATS6=1	MAVLink framing	Standard MAVLink
ATS8 / ATS9	Band min/max frequency (kHz)	Per your country’s regulations — in Australia, the 915–928 MHz class licence

Saving:

Command	Function
AT&W	Write to EEPROM — without this, changes are lost on reboot
ATZ	Reboot the radio
ATO	Exit AT mode, resume data

Troubleshooting

• Radio dead / no lights: airborne radio needs the flight battery (servo-rail powered), not USB.
• +++ gets no OK: line ending must be None for +++; MAVLink may still be streaming (check SERIAL1_OPTIONS 1024); wait the full 30 s after enabling passthrough.
• Endless green flashing, never solid: the two radios don’t match — NetID, air rate, band, or encryption mismatch. An encrypted radio will never link to an unencrypted one.
• Terminal prints endless # garbage: MAVLink is still on the port — passthrough isn’t active.

Refer to the RFDesign RFD900x/ux manuals for the full register reference.