⚠ Legal Warning The GPS-SIM file generation feature is intended solely for experimental and educational purposes in a controlled RF environment (e.g. Faraday cage, shielded lab). Broadcasting GPS signals — even simulated ones — may be illegal in your jurisdiction and can interfere with navigation systems, aviation, and emergency services. You are solely responsible for ensuring compliance with all applicable local laws and regulations before use. The authors of this software accept no liability for any misuse.
A Windows GUI application that downloads GPS broadcast ephemeris (BRDC) files from NASA CDDIS and optionally generates PortaPack Mayhem GPS-SIM files (.C8 + .TXT).
- GUI interface — no command line needed
- Downloads RINEX 2 (
brdc*.YYn) or RINEX 3 (BRDC00IGS_R_*) navigation files - Date picker with automatic Day-of-Year (DOY) calculation
- Auto-decompresses
.gzfiles - Optional
.brdcextension rename - GPS-SIM output: generates
.C8+.TXTfiles ready for PortaPack Mayhem- Configurable latitude, longitude, height, sample rate, duration
- Default TX parameters pre-filled (GPS L1: 1575.420 MHz)
- NASA Earthdata Login authentication
- Auto-installs
requestsdependency on first run
- Python 3.8+
- A free NASA Earthdata account
- (For GPS-SIM only) gps-sdr-sim compiled executable
- Double-click
BRDC_Downloader.bat— the GUI opens (no console window) - Enter your Earthdata username and password
- Select the date
- Choose RINEX format and output options
- (Optional) Enable GPS-SIM Output, set your location and parameters
- Click Download
To create a Desktop shortcut, run Create_Desktop_Shortcut.bat once.
When enabled, after downloading and decompressing the BRDC file, the app runs gps-sdr-sim to generate:
| File | Description |
|---|---|
gpssim.C8 |
Raw IQ baseband GPS signal (8-bit signed) |
gpssim.TXT |
TX parameters: center frequency + sample rate |
The .TXT file format:
center_frequency=1575420000
sample_rate=2600000
Download or compile from: https://github.com/osqzss/gps-sdr-sim
Point the app to gps-sdr-sim.exe using the Browse button.
| Parameter | Default | Notes |
|---|---|---|
| Center frequency | 1575.420 MHz | GPS L1, fixed |
| Sample rate | 2.6 MHz | Recommended for PortaPack |
| Latitude / Longitude | 0.0 / 0.0 | Change to your location |
| Height | 0 m | Meters above sea level |
| Duration | 300 s | 5 minutes |
| Format | Example filename | Note |
|---|---|---|
| RINEX 2 | brdc0970.26n |
Standard GPS nav, year 2026 |
| RINEX 3 | BRDC00IGS_R_2026097... |
Multi-constellation |
| .brdc | brdc0970.brdc |
Same content, renamed |
CDDIS requires a free Earthdata account. Register at:
https://urs.earthdata.nasa.gov/users/new
Your credentials are never stored — entered each session in the GUI.
MIT — see LICENSE