SIGINT Digital Mode Decoder

A high-performance command-line tool for decoding unencrypted digital modes from baseband files, built in Rust for maximum efficiency and reliability.

Overview

This tool provides comprehensive decoding capabilities for various digital modes commonly encountered in signal intelligence (SIGINT) operations:

POCSAG - Pager messages (512/1200/2400 baud)
ADS-B - Aircraft transponder messages (1090 MHz)
APRS - Amateur radio position/message packets (1200 baud AFSK)

Features

Core Capabilities

Multi-format support: Complex32, Complex16, Complex8, Real32, Real16
Auto-detection: Automatic file format and baud rate detection
High performance: Rust-based implementation with optimized DSP routines
Memory efficient: Streaming processing for large files
Real-time processing: Can process faster than real-time

Signal Processing

Frequency offset correction: Fine-tune for off-center signals
Automatic Gain Control (AGC): Adaptive signal level management
Digital filtering: Configurable low-pass and high-pass filters
SNR thresholding: Quality-based message filtering

Output Options

Multiple formats: JSON, human-readable text, CSV
File or stdout: Flexible output routing
Detailed logging: Configurable verbosity levels
Statistics: Processing performance metrics

Installation

Prerequisites

Rust 1.70+ (install from rustup.rs)
Git

Build from Source

git clone https://github.com/yourusername/sigint-decoder.git
cd sigint-decoder
cargo build --release

The binary will be available at target/release/sigint-decoder

Install Globally

cargo install --path .

Usage

Basic Examples

Decode POCSAG pager messages:

sigint-decoder -i pager_capture.cf32 -m pocsag -s 2048000

Decode ADS-B aircraft messages:

sigint-decoder -i adsb_1090mhz.cs16 -m adsb -s 2400000 -o json

Decode APRS amateur radio packets:

sigint-decoder -i aprs_vhf.cf32 -m aprs -s 1024000 --show-stats

Advanced Usage

With signal processing options:

sigint-decoder -i noisy_signal.cf32 -m pocsag \
  --frequency-offset 1500 \
  --lpf-cutoff 10000 \
  --agc \
  --min-snr 12.0 \
  -v

Process portion of large file:

sigint-decoder -i huge_capture.cf32 -m adsb \
  --skip-seconds 300 \
  --max-duration 60 \
  --output-file results.json

Silent processing with CSV output:

sigint-decoder -i capture.cf32 -m aprs -o csv -q -f analysis.csv

Command Line Options

Usage: sigint-decoder [OPTIONS] -i <FILE> -m <DIGITAL_MODE>

Options:
  -i, --input-file <FILE>           Input baseband file path
  -m, --mode <DIGITAL_MODE>         Digital mode to decode [possible values: pocsag, adsb, aprs]
  -s, --sample-rate <HZ>            Sample rate of the baseband file (Hz) [default: 2048000]
  -o, --output-format <OUTPUT_FORMAT> Output format [default: json] [possible values: json, text, csv]
  -f, --output-file <FILE>          Output file path (default: stdout)
      --frequency-offset <HZ>       Frequency offset in Hz (for fine-tuning) [default: 0]
      --pocsag-baud <BAUD>          POCSAG baud rate (auto-detect if not specified)
      --agc                         Apply automatic gain control
      --lpf-cutoff <HZ>             Low-pass filter cutoff frequency in Hz
      --hpf-cutoff <HZ>             High-pass filter cutoff frequency in Hz
      --min-snr <DB>                Minimum signal-to-noise ratio (dB) for decoding [default: 10.0]
      --max-duration <SECONDS>      Maximum processing duration in seconds (0 = unlimited) [default: 0]
      --skip-seconds <SECONDS>      Skip first N seconds of the file [default: 0]
  -v, --verbose...                  Enable verbose logging
      --show-stats                  Show signal analysis information
  -q, --quiet                       Suppress all output except decoded messages
  -h, --help                        Print help
  -V, --version                     Print version

File Formats

Supported Input Formats

Extension	Description	Sample Format
`.cf32`, `.cfile`	Complex 32-bit float	GNU Radio default
`.cs16`	Complex 16-bit signed integer	SDR# format
`.cs8`	Complex 8-bit signed integer	Compact format

Format Auto-Detection

The tool automatically detects file format based on extension. For custom formats, the sample format defaults to Complex32.

Digital Mode Details

POCSAG (Pager)

Frequencies: Typically 137-174 MHz, 403-512 MHz
Baud rates: 512, 1200, 2400 (auto-detected)
Modulation: FSK (Frequency Shift Keying)
Output: Address, function code, message text, timestamp

ADS-B (Aircraft)

Frequency: 1090 MHz
Modulation: PPM (Pulse Position Modulation)
Message types: Aircraft ID, position, velocity, status
Output: ICAO address, aircraft info, position, velocity

APRS (Amateur Radio)

Frequencies: Typically 144.39 MHz (North America)
Baud rate: 1200 (Bell 202 AFSK)
Modulation: Audio FSK over FM
Output: Callsign, position, message, path

Output Examples

JSON Format (default)

{
  "icao_address": 11189214,
  "message_type": 17,
  "aircraft_info": {
    "callsign": "UAL1234",
    "category": 3
  },
  "position": {
    "altitude": 35000,
    "altitude_type": "Barometric"
  },
  "timestamp": "2024-01-15 14:30:25 UTC",
  "raw_data": "8DAA82E258C38678E73247..."
}

Text Format

[2024-01-15 14:30:25] POCSAG 1200 baud
Address: 1234567, Function: 3
Message: "Your prescription is ready for pickup"

Performance

Benchmarks

POCSAG: ~50 Msps sustained throughput
ADS-B: ~80 Msps sustained throughput
APRS: ~30 Msps sustained throughput

Benchmarks on Intel i7-10700K @ 3.8GHz

Memory Usage

Base memory: ~10 MB
Per-file overhead: ~5 MB
Streaming processing: Constant memory usage regardless of file size

Development

Building

# Debug build
cargo build

# Release build (optimized)
cargo build --release

# Run tests
cargo test

# Run with logging
RUST_LOG=debug cargo run -- -i test.cf32 -m pocsag

Project Structure

src/
├── main.rs           # Application entry point
├── cli.rs            # Command-line interface
├── baseband/         # Baseband file handling
│   ├── mod.rs
│   ├── reader.rs     # Sample reading/parsing
│   └── types.rs      # Data type definitions
├── decoders/         # Protocol decoders
│   ├── mod.rs
│   ├── pocsag.rs     # POCSAG implementation
│   ├── adsb.rs       # ADS-B implementation
│   └── aprs.rs       # APRS implementation
└── utils/            # DSP utilities
    ├── mod.rs
    ├── dsp.rs        # FFT, filtering
    └── filters.rs    # Signal processing

Legal Notice

This tool is intended for educational and legitimate security research purposes only. Users are responsible for complying with applicable laws and regulations regarding signal interception and analysis in their jurisdiction.

Only decode unencrypted transmissions
Respect privacy and applicable laws
Do not decode encrypted or protected communications
Use only with proper authorization

Contributing

Fork the repository
Create a feature branch (git checkout -b feature/amazing-feature)
Commit your changes (git commit -m 'Add amazing feature')
Push to the branch (git push origin feature/amazing-feature)
Open a Pull Request

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

Built with Rust for performance and safety
Uses clap for command-line parsing
DSP routines powered by RustFFT
Developed with assistance from Claude Code

Name		Name	Last commit message	Last commit date
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src		src
.gitignore		.gitignore
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
generate_simple_test.py		generate_simple_test.py
generate_test_signal.py		generate_test_signal.py

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