GPREDICT: A Beginner’s Guide to Features and SetupGPredict is a free, open-source application for satellite tracking that provides real-time visualization of satellites, antenna tracking control, pass predictions, and a range of tools useful for amateur radio operators, educators, researchers, and hobbyists. This guide covers GPredict’s key features, system requirements, installation, basic configuration, and practical tips to get you tracking satellites confidently.
What GPredict Does (Overview)
- Real-time satellite tracking: GPredict shows the current positions of satellites relative to your chosen ground station and a global map or polar view.
- Pass prediction and alerts: It calculates upcoming satellite passes for any location and can notify you when a target satellite is about to rise.
- Antenna control: GPredict can interface with many rotator controllers (using protocols like Hamlib, KPA, and custom serial commands) to physically steer antennas.
- Doppler shift correction: For radio users, GPredict outputs frequency correction data to external software or radios so you can compensate for Doppler shifts during passes.
- Multiple tracking engines: Support for various orbit prediction models (SGP4/TLEs) and the ability to import TLEs automatically.
- Custom satellite lists and grouping: Organize satellites by usage (e.g., NOAA, ISS, amateur radio) and save favorite groups for quick access.
- Observation logging and scripting: Log passes, automate tasks with scripts, and extend behavior with plugins where supported.
System Requirements and Supported Platforms
GPredict runs on major desktop platforms:
- Linux: Primary platform; available in many distributions’ repositories (Debian/Ubuntu, Fedora, Arch).
- Windows: Builds exist and can be installed via binaries or via package managers like MSYS2.
- macOS: Community builds and instructions are available; official macOS packages may be less common.
Minimum hardware requirements are modest: a modern CPU, 512 MB–1 GB RAM, and a GPU capable of basic 2D/3D rendering for the map and sky views. For antenna control and radio integrations, appropriate serial/USB interfaces are needed.
Installation
Below are concise installation paths for common platforms.
Linux (Debian/Ubuntu):
sudo apt update sudo apt install gpredict Fedora:
sudo dnf install gpredict Windows:
- Download the latest Windows installer from the GPredict project page or use MSYS2 packages if available. Run the installer and follow prompts.
macOS:
- Use Homebrew if a formula is available, or follow community build instructions on the GPredict website and compile from source.
If the packaged version in your distro is outdated, building from source ensures the latest features. Building requires development tools (gcc/clang, make, CMake), GTK libraries, and dependencies listed in GPredict’s README.
First Launch and Basic Configuration
- Launch GPredict. The default layout typically shows a world map, a polar/elevation view, and a satellite list.
- Set your ground station location:
- Open Preferences → Ground Stations → Add.
- Enter latitude, longitude, elevation, and an optional name. Accuracy within a few meters is fine for visualization; antenna control benefits from exact coordinates.
- Import or update TLEs (Two-Line Element sets):
- Use the built-in TLE updater (Preferences → TLE → Update) or manually import TLE files.
- TLEs age over time; refresh regularly for accurate tracking.
- Add satellites to your tracking list:
- Search the master catalog, select satellites (ISS, NOAA, amateur satellites), and add them to a group or observation list.
- Choose prediction settings:
- Configure minimum elevation cutoff (e.g., 10°–20°) so GPredict ignores low, unusable passes.
- Set pass prediction time window (next 24–72 hours).
Using the Interface: Views and Controls
- Map view: Shows satellite ground tracks and footprints. You can zoom, pan, and toggle layers (day/night terminator, satellite footprints).
- Azimuth/Elevation (polar) view: Visualizes elevation vs azimuth for current or upcoming passes. Useful to judge antenna clearance and obstructions.
- Satellite list: Displays real-time data for each tracked satellite (azimuth, elevation, range, range rate, next pass start/stop).
- Pass table and timeline: Lists upcoming passes with start/peak/end times, duration, and max elevation. Sort and filter by group or satellite.
- Context menus: Right-click satellites for quick actions like “Track”, “Center map”, “Show pass details”, or “Start logging”.
Antenna and Radio Integration
A key strength of GPredict is controlling hardware and coordinating with radios:
- Rotator control:
- GPredict supports Hamlib and several rotator protocols. In Preferences → Rotors, choose the interface (serial, network), port, baud rate, and protocol.
- Test rotation commands in a safe environment to ensure correct orientation and limits.
- Radio/Doppler control:
- Send frequency correction to radios using CAT interfaces or external programs. GPredict can output Doppler corrections to applications/scripts via UDP/TCP or by controlling the radio directly when supported.
- Common integration setups include GPredict → hamlib → rigctld or GPredict → external script → radio driver.
- Tracking delays:
- Account for mechanical lag of your rotator and command latency in software settings (slew rate limits, smoothing).
Practical Examples
- Tracking the ISS for a live video downlink:
- Add ISS to your list, set antenna rotator profile, enable Doppler correction to your radio, and use the pass table to prepare camera/receiver equipment 2–3 minutes before rise.
- Receiving NOAA weather images:
- Add NOAA APT satellites, set audio recorder/demodulator software to receive audio during passes, and use GPredict’s pass notifications to start recording automatically.
- Amateur satellite (FM/SSB) contacts:
- Configure Doppler output to your HT or SDR software, and test by tracking a known FM repeater satellite on a low-elevation pass.
Troubleshooting Common Issues
- Stale or inaccurate TLEs: Update TLEs frequently; for critical contacts use sources with recent epochs.
- Rotator commands not working: Verify serial connections, correct protocol, and that no other software is controlling the rotator. Use manual test commands.
- Doppler correction jumps: Use smoothing settings or interpolation if receiver control blips; ensure time synchronization (NTP) on your computer.
- Incorrect ground station coordinates: Double-check GPS-derived coordinates and input format (decimal degrees vs degrees/minutes).
Tips and Best Practices
- Keep system time synced with NTP for accurate pass times and Doppler corrections.
- Maintain an organized satellite group list tailored to your interests (weather, ISS, amateur) for quick access.
- Test hardware control (rotator, radio) with segments of motion while the antenna is safe to move.
- Use logging for post-pass analysis and to build a history of receptions/contacts.
- Read the GPredict changelog and community forums for setup recipes specific to your radio/rotator hardware.
Extending GPredict
- Use scripts to automate tasks like starting a recording, adjusting SDR software, or sending notifications to mobile devices.
- Explore plugins or community forks for enhanced GUI features, improved hardware compatibility, or additional prediction models.
- Integrate with other amateur radio tools (e.g., Gpredict → Direwolf for APRS, or GPredict → Gqrx/SDR for real-time decoding).
Resources
- GPredict documentation and README for build instructions, protocol details, and advanced configuration examples.
- Community forums and Git repositories for user-contributed scripts, rotator setups, and troubleshooting tips.
GPredict is a powerful tool for anyone interested in satellites — from casual observers to seasoned amateur radio operators. With accurate TLEs, correct ground station configuration, and careful hardware setup, GPredict enables reliable real-time tracking, antenna control, and Doppler management to support a wide range of satellite activities.
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