Bending the Flipper Zero’s CC1101 Into an APRS Transmitter

Over on GitHub, Richard YO3GND has released a Flipper Zero APRS TX application that pushes the device's onboard CC1101 radio into transmitting Bell 202 AFSK, despite FM not really being what that chip was designed to do.

The author is upfront that this is very impractical: it is transmit-only, the transmitted signal is imperfect and not recognized by some APRS hardware (software decoders seem to work well), and the joystick text entry is painful.

The implementation builds the full APRS stack on the Flipper itself, handling packet type construction, AX.25 framing, and waveform generation in software, and supports status, position, bulletins, and direct APRS messages. There are also some low-level settings exposed in the UI, including 300 baud operation, preamble length, and lead-in tuning, alongside the standard APRS settings.

While this may be impractical for any real use case, the idea of implementing the protocol properly on a constrained device is an interesting read.