radfly

radfly is a self-hosted, SDR-based listening server for AM medium wave and short-wave radio stations with a simple web frontend. radfly is built on ZigRadio and http.zig, and currently supports rtl-sdr and AirSpy HF+ SDRs.

The web frontend streams audio, supports scanning, bookmarks, and configuring options like audio bandwidth and AGC mode. radfly can be run on Raspberry Pi 4 and similar single-board computers.

Building

radfly requires Zig version 0.14.

$ git clone https://github.com/vsergeev/radfly.git
$ cd radfly
$ zig build

Install optional (but recommended) acceleration libraries:

sudo apt install -y libvolk-dev libliquid-dev libfftw3-dev on Debian-based systems
sudo pacman -S libvolk liquid-dsp fftw on Arch Linux-based systems

Running

Start radfly with an SDR source, e.g. mock (for testing), rtlsdr, or airspyhf:

$ ./zig-out/bin/radfly --source airspyhf

radfly will be accessible at http://localhost:8000.

Local Network

Due to the dependency on AudioWorklet for streaming audio in the browser, the radfly frontend must be served over a secure context (HTTPS) to be accessed by other machines on a local network. Caddy can be used as a secure reverse proxy for this.

Start caddy (replace radio-pi4 with your machine's hostname):

$ sudo caddy reverse-proxy --from radio-pi4.local --to :8000

radfly will now be accessible on the local network at https://radio-pi4.local.

Certificate Warning

caddy uses self-signed certificates for *.local hostnames, which can't be trusted automatically by browsers and results in an insecure connection warning. To remove this warning, import caddy's generated root certificate, located at /root/.local/share/caddy/pki/authorities/local/root.crt, into your browser's certificate manager.

Usage

Usage: radfly [options]

Radio Configuration
  --source <mock,rtlsdr,airspyhf>     SDR Source (default mock)
  --bias-tee <true/false>             Bias tee (default false)
  --tune-offset <value in KHz>        Tune offset (default 50 KHz)
  --initial-frequency <value in KHz>  Initial frequency (default 5000 KHz)

Server Configuration
  --http-port <port number>           HTTP listening port (default 8000)
  --http-address <address>            HTTP listening address (default 127.0.0.1)

Miscellaneous
  --help                              Display usage
  --version                           Display version
  --debug                             Enable debug mode

Design

The ZigRadio flowgraph consists of audio demodulation and power measurement signal chains that feed into their respective ApplicationSink. Audio and power samples are consumed by an application thread and pushed to active clients via WebSockets. An RPC protocol over WebSockets allows clients to scan, tune, and change various parameters in the flowgraph.

flowchart LR
    A[Source] --> B[TunerBlock]
    B --> G[LowpassFilterBlock]
    subgraph s2 [Power Measurements]
    G --> H[PowerMeterBlock]
    H --> I[ApplicationSink]
    end
    B --> C[AMEnvelopeDemodulator]
    subgraph s1 [Audio]
    C --> D[AGCBlock]
    D --> E[DownsamplerBlock]
    E --> F[ApplicationSink]
    end

Tests

Run unit tests with:

$ zig build test

License

radfly is MIT licensed. See the included LICENSE file.

Dependencies

README