GSoC 2025 FM Receiver App - 13-Week Progress Summary

Project Overview

Project: User-friendly FM Broadcast Receiver Application with RDS and Spectrum Scanning
Organization: GNU Radio
Timeline: May 30 - August 25, 2025 (13 weeks)
Repository: GNU-Radio-FM-App
Documentation: Project Documentation
Tutorial: GNU Radio Tutorial

Gallery

Key Achievements

Core Application Development

Complete PyQt5-based GUI with home view, debug view, and SDR configuration
Integrated GNU Radio flowgraphs with Python application for real-time FM reception
RDS (Radio Data System) integration using gr-rds module for metadata extraction
Multi-threaded architecture preventing UI freezing during scanning operations
Configuration management system for saving user settings and station lists

Advanced Features

Automated FM station detection using power spectral density analysis with frequency raster alignment
Multiple simultaneous recording capability with hierarchical GNU Radio blocks
Real-time audio visualization and spectrum analysis in debug view
SDR device auto-detection with SoapySDR integration
Station management with add/delete/record functionality

Technical Implementation

Modular project structure with clear separation of GUI, core processing, and utilities
Custom GNU Radio embedded blocks for station detection and signal processing
Frequency scanning algorithm capable of detecting 23+ FM stations
Audio recording system with WAV file output
Real-time spectrum waterfall and constellation diagrams

Weekly Progress Breakdown

Weeks 1-2: Foundation & Design

Established comprehensive project directory structure
Created UI mockups in Figma and implemented basic PyQt5 interface
Set up development environment with GNU Radio integration

Weeks 3-4: Core FM Reception

Implemented basic FM receiver flowgraph integration
Added RDS panel integration from gr-rds module
Developed initial frequency scanning approach using PSD analysis

Weeks 5-6: Station Detection

Built sophisticated FM scanner using frequency bin power summation
Implemented threshold detection with peak finding algorithms
Added debug view with RF band, waterfall, RDS, and audio visualizations
Integrated 19kHz pilot tone detection for station verification

Weeks 7-8: Code Quality & Features

Code formatting and documentation using pylint, isort, and mkdocs
Added audio visualization and improved RDS panel integration
Resolved import issues with embedded GNU Radio blocks

Weeks 9-10: Recording & Configuration

Implemented audio recording functionality with WAV sink integration
Added top menu bar and file path selection
Created SDR device configuration manager with auto-detection
Fixed toggle button state management during scanning

Weeks 11-12: Multi-Recording & Polish

Developed multiple simultaneous recording feature using hierarchical blocks
Added station button widgets with record/delete functionality
Implemented notification system for bandwidth constraints
Created auto-select SDR functionality for single-device setups

Week 13: Documentation & Finalization

Comprehensive documentation with mkdocs GitHub pages deployment
Migrated from deprecated Osmocom to soapy_custom_source blocks
Final bug fixes and README improvements across all directories

Week 14: Write Tutorial in GNU Radio Tutorials Section

Technical Challenges Overcome

SDR Resource Management

Problem: GNU Radio flowgraphs couldn’t share SDR access simultaneously
Solution: Implemented selector blocks to switch between scan/play modes within single flowgraph

Station Detection Accuracy

Problem: Simple peak detection failed without external LNA amplification
Solution: Developed normalized power summation approach aligned to FM frequency raster (100kHz intervals)

Multi-threading Integration

Problem: Blocking operations froze the GUI during spectrum scanning
Solution: Created QThread-based scanning monitor with progress reporting

Import System Conflicts

Problem: GRC-generated code had import path issues with embedded blocks
Solution: Manual module registration in sys.modules before flowgraph import

System Architecture

Directory Structure

fm-receiver-app/
├── docs/              # MkDocs documentation
├── flowgraphs/        # GNU Radio .grc files and generated Python
├── src/fm_receiver/   # Main application code
│   ├── gui/          # PyQt5 interface components
│   ├── core/         # GNU Radio integration
│   └── utils/        # Helper functions and scanning logic
├── tests/            # Unit and integration tests
└── examples/         # Sample configurations

Key Components

Main Window: Central GUI controller with view management
FM Scanner: Embedded GNU Radio block for station detection
Multiple Recorder: Hierarchical blocks for simultaneous recording
Config Manager: Settings persistence and SDR device management
Debug View: Real-time visualization with spectrum plots

Performance Metrics

Detection Capabilities

Station Detection: Up to 23 FM stations detected automatically
Frequency Range: 87.5-108.0 MHz FM broadcast band
Detection Method: Power spectral density with 100kHz raster alignment
Accuracy: All detected stations verified through manual listening

Recording Features

Simultaneous Recordings: Up to 3 stations within 2MHz RTL-SDR bandwidth
Audio Quality: 48kHz sampling rate with WAV output
Bandwidth Constraints: Automatic validation prevents out-of-range recording

Real-time Processing

FFT Size: 1024-point FFT for spectrum analysis
Update Rate: Real-time spectrum waterfall and audio visualization
Threading: Non-blocking GUI with background processing threads

Future Enhancement Opportunities

Short-term Improvements

Dynamic Sample Rate Control: Allow users to change SDR sample rates without flowgraph reconstruction
Enhanced FM Detection: Statistical noise testing to prevent false positives
Station Strength Indicators: Display signal strength metrics for detected stations

Long-term Extensions

SCA Decoding: Subsidiary Communications Authorization support
Network Integration: Web SDR connectivity for remote reception
Advanced Audio Processing: Stereo/mono switching, audio effects

Documentation & Resources

User Documentation

GitHub Pages: Comprehensive tutorials and API documentation
README Files: Directory-specific documentation for contributors
Installation Guide: Step-by-step setup instructions
Usage Examples: Sample configurations for different SDR hardware

Developer Resources

Code Documentation: Comprehensive docstrings and type hints
Testing Framework: Unit tests for core functionality
Contribution Guidelines: Clear project structure for new developers

Conclusion

The FM Receiver Application successfully demonstrates a complete software-defined radio solution combining GNU Radio’s signal processing capabilities with a user-friendly PyQt5 interface. The project achieved all primary objectives including automated station detection, RDS integration, recording functionality, and advanced debugging tools.

The modular architecture and comprehensive documentation provide a solid foundation for future enhancements and community contributions. The application serves as both a practical FM receiver tool and an educational resource for SDR development with GNU Radio.

Final Status: Project completed successfully with all core features implemented and documented. The application is ready for end-user deployment and continued community development.

Useful Links

End of My GSoC journey