mySatComm

Homebrew groundstation for receiving data from satellites. Servos are controlled via Raspberry Pi; DSP is handled through the GNU Radio and GPredict. Go here to see STL models in GitHub.

Project Overview

This is a farm-to-table amateur radio project composed of 3 major subprojects:

• Mechanical Design
  • Antenna Rig
  • Orientation Controller
• Command & Control Software
  • Servomotor low-level control
  • GPredict command interface
  • Rotator trajectory generation
• Digital Signal Processing
  • Radio demodulation and doppler shifting
  • Information decoding

Installation

Clone this repo to your Raspberry Pi and run install.sh. All Python dependencies will be installed in a virtual environment at $HOME/.satcomm. Additionally,

To uninstall, run the corresponding uninstall.sh script.

On your PC, install GPredict, GNU Radio, and download the SDR folder.

Using the programs

1. Create a GPredict module tracking some satellites of interest. Be sure to look at the manual and website.

2. Configure GPredict to interface with your Raspberry Pi as a networked rotator (you'll need its IP address).

3. Configue GPredict to work with your SDR. If you don't have a go-to, I recommend using the NooElec NESDR Mini 2.

4. Wait for a satellite to pass within range, then activate GPredict radio and rotator control programs and run ./run.sh on your Pi.

5. Watch it go!

Software/Retailer Links

• GPredict - Satellite tracking and antenna actuation software
• PiGPIO - Provides hardware-timed GPIO control on Raspberry Pi
• Raspberry Pi - Hobbyist-oriented single-board computer
• SolidWorks - CAD software
• SainSmart - Robotic components manufacturer

Project Subfolders

• Antenna Design
• Az-El Controller
• Control Software
• Data Reception
• Data Decoding

Mechanical Quick Reference

• GitHub-viewable Models
• Antenna Rotator
• Base Dipole
• Bill of Materials

Software Quick Reference

• HamLib (GPredict Command Library)
• HamLib on RPi
• Servo Characterization

Design Decisions

Antenna

• 3-element linearly polarized yagi antenna
  • Directionality recommended for satellite reception
  • Circular polarization is annoying (for me) to get right
• Homebrew dipole antenna base made from PVC, AWG14 wire, and screws
  • COTS parts increase accessiblity and homebrew aesthetic
  • Thicker wire chosen for increased rigidity

Controller

• Custom housing
  • Convenient mount point for rotator
  • Minimizes wiring connecting Pi and servos
  • 3D printed for rapid prototyping
• Solderboard Pi shield
  • More reliable wiring of servo battery power
  • Faster connect/disconnect of servos from Pi

Software

• GPredict
  • Open source satellite tracking software
  • Computes necessary antenna orientation automatically
  • Sends antenna orientation commands over TCP/IP
  • Manual here
• PiGPIO
  • Provides almost-hardware-timed PWM (important for servo control)
  • PWM less noisy and more reliable than RPi-GPIO or wiringPi
  • Simple Python interface

SDR Sources & Acknowledgements

• Wolfgang Nagele for his GRC Gpredict Doppler shift correction block
• Alexandru Csete for this tutorial for an APT decoder in GRC

Author

Marion Anderson - lowdrant

License

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