texysexr/hackrf-fm-encoder

This repository provides a command-line tool that converts ordinary audio files into a special format used by HackRF One and PortaPack radio devices. These devices can transmit radio signals, and the tool prepares audio so it can be played back as FM radio through that hardware. Supported input formats include MP3, WAV, FLAC, and M4A. The tool runs on Python and relies on a few helper programs. NumPy and SciPy handle the math involved in turning sound into radio signal data. Rich provides a clean interface in the terminal. FFmpeg, a separate program you install on your computer, handles the initial audio conversion when needed. You also need Python 3.8 or newer, and the tool works on Windows, Linux, and macOS. Using it is straightforward. You place your audio files in the same folder as the script and run it. The tool shows a list of your audio files and asks you to pick one. Then you choose from four presets: PortaPack FM Broadcast at 500 kHz for most users, High Fidelity at 1 MHz for best quality, Low Storage at 250 kHz for smaller files, or a fully custom option. You enter a center frequency in megahertz and a name for the output file. The tool then processes the audio through several steps. It converts the file to WAV if needed, normalizes the volume, applies FM pre-emphasis filtering for better sound quality, resamples the audio, and generates the radio signal data. It saves a .c8 file containing that data and a .txt file with metadata the PortaPack device needs, including the frequency and sample rate you chose. To play the result on a PortaPack, you copy both files to the SD card and select the .c8 file from the Replay app. If you are using a HackRF directly, the tool prints the exact command you need to run for playback. The project is open source under the MIT License and welcomes contributions.