Web-based Software Defined Radio. Browser-native alternative to SDR++.

Connects to an RTL-SDR dongle via rtl_tcp, streams raw IQ data to the browser, and performs all signal processing (FFT, FM demodulation) client-side via Rust compiled to WebAssembly.

[Machine with SDR dongle]                     [Browser]
  rtl_tcp :1234                                 WASM DSP (Web Worker)
       ↓                                         ├── FFT → spectrum/waterfall
  backend (proxy) :8080  ←── WebSocket ──→        └── WFM demod → audio
  (raw IQ passthrough)

The backend is a thin TCP→WebSocket proxy with zero per-client DSP cost. All heavy processing runs in the browser.

• Real-time spectrum analyzer with frequency axis and peak hold
• Scrolling waterfall spectrogram
• Wideband FM demodulation with browser audio playback
• All DSP in browser via Rust→WASM (FFT, FIR filters, FM discriminator, de-emphasis)
• Frequency tuning and gain control (manual + AGC)
• Keyboard shortcuts (arrow keys for tuning, Space for play/stop)
• Auto-reconnection with exponential backoff
• Multi-client support (proxy scales to many clients)

• RTL-SDR dongle + rtl_tcp (from librtlsdr)
• Rust toolchain (1.75+) with cargo available on your PATH
• wasm-pack (cargo install wasm-pack)
• Node.js (20+)

# Terminal 1: start rtl_tcp
rtl_tcp -a 127.0.0.1

# Terminal 2: start backend (proxy)
cd backend
cargo run --release -- --frequency 81300000  # J-WAVE 81.3 MHz

# Terminal 3: build WASM + start frontend
wasm-pack build --target web --out-dir ../frontend/src/wasm wasm-dsp
cd frontend
npm install
npm run dev --turbopack
# Open http://localhost:3000

Thin TCP→WebSocket bridge. Connects to rtl_tcp, streams raw IQ data to browsers, relays control commands back. No DSP.

Key dependencies: tokio, tokio-tungstenite, clap, tracing

All DSP runs in the browser via WebAssembly, inside a Web Worker (off the main thread):

u8 IQ @ 2.048 Msps (from WebSocket)
  → [FFT branch]   2048-pt FFT → dB magnitude → spectrum/waterfall (20 fps)
  → [Audio branch]  lowpass + decimate ÷8 → 256 kHz
                    → atan2 FM discriminator
                    → lowpass + decimate ÷5 → ~48 kHz
                    → de-emphasis 50μs (Japan)
                    → f32 PCM → Web Audio API

~200 lines of custom DSP. Only external DSP dep: rustfft + num-complex. WASM binary: ~217 KB.

Single connection on ws://localhost:8080, multiplexed:

• Binary frames: 1-byte type tag + payload
  • 0x01 Raw IQ: uint8 interleaved IQ pairs
  • 0x03 Status: JSON (tuner info, connection state)
• Text frames: JSON control commands (set_frequency, set_gain, set_agc)

# Build and test everything
cargo test                    # Rust workspace tests (backend + wasm-dsp)
cargo fmt --all               # format Rust code
cargo clippy --all-targets --all-features -- -D warnings

# Backend
cd backend
RUST_LOG=debug cargo run --release

# WASM DSP
wasm-pack build --target web --out-dir ../frontend/src/wasm wasm-dsp

# Frontend
cd frontend
npm install
npm run dev --turbopack       # dev server
npm run build                 # production build
npm run lint                  # lint

If cargo is not found, make sure your Rust toolchain is installed and loaded into your shell first.

MIT