Note

This project was formerly known as gps-time-sync.

ChronoGPS

GPS / NTP Time Synchronization Tool for Windows

A tool to accurately synchronize your Windows PC clock using a GPS receiver or NTP server.
Designed for high-precision time alignment required for FT8 and other digital amateur radio modes.
Runs safely in Monitor-Only mode even without administrator privileges.

🌐 日本語 README

Design Philosophy

ChronoGPS is designed with one simple goal:
to provide accurate time with minimal user intervention.

Use GPS or NTP depending on availability and environment
Perform synchronization safely in the background while keeping the UI stable
Provide a reliable time reference for FT8 and measurement use cases

Rather than visual effects, the focus is on accuracy, stability, and long-term operation.

For detailed explanations of ChronoGPS design decisions and synchronization behavior, please refer to the FAQ: 👉 FAQ (English)

Typical Use Cases

FT8 / FT4 operation requiring accurate PC time
Portable / field operation (SOTA / POTA) without Internet access
Long-term clock monitoring on a general-purpose Windows PC
GNSS-based UTC reference with an inexpensive USB receiver

Why ChronoGPS?

If you are interested in the design philosophy behind ChronoGPS —
including transparency, how administrator privileges are handled, and the idea of a monitor-only mode —
please see the detailed discussion below:

🔗 Why ChronoGPS (Discussion): #3

Features

🌐 NTP Sync (RFC 5905) — 64-bit timestamps, offset/delay calculation via t1/t2/t3/t4, millisecond-level precision
🛰️ GPS Sync — Off / Instant / Scheduled modes, RMC-based UTC acquisition, duplicate sync prevention
Scheduled mode uses a GPS-reception-triggered approach with median jitter filtering.
This reduces jitter injection while allowing long-term drift monitoring.
⏱️ FT8 Time Offset — Fine-tune clock in ±0.1s steps, designed for digital mode operation
📡 Satellite View — Real-time display of GPS / GLONASS / BeiDou / Galileo / SBAS / QZSS
🔒 Non-Admin Support (v2.5 enhanced) — Starts in Monitor-Only mode by default. Elevate only when sync is needed via the on-screen banner
🧵 Thread-Safe GUI — Worker thread + Queue + main thread updates prevent Tkinter freezes
🌍 16 Languages — Japanese, English, French, Spanish, German, Chinese (Simplified/Traditional), Korean, Portuguese, Italian, Dutch, Russian, Polish, Turkish, Swedish, Indonesian
🖥️ Windows-Native UX — System tray support, the close (X) button minimizes to the system tray, taskbar icon

Screenshots

Main window during GNSS synchronization. Time Error: −0.001 s.

Satellite information view (GPS / GLONASS / BeiDou / Galileo / SBAS / QZSS).

Operation Modes (v2.5+)

Starting with v2.5, the UAC dialog at launch has been removed.
ChronoGPS always starts in Monitor-Only mode by default.
Elevation is only requested when the user explicitly wants sync.

At Launch (Default: Monitor-Only)

No UAC dialog is shown
GPS reception, satellite view, and NTP display are available immediately
A banner at the top of the window shows: "Unlock Sync Features (Restart as Administrator)"

When You Need Time Sync

Click the banner button → UAC dialog appears → Restart as administrator
If you cancel the UAC dialog, Monitor-Only mode continues — the process is not terminated
After elevation, the banner disappears and GPS/NTP sync becomes available

Command-Line Launch

# Monitor-Only mode (default)
.\ChronoGPS.exe

# Sync mode (banner still appears if not admin)
.\ChronoGPS.exe --mode=sync

Requirements

Windows 10 / 11
Python 3.11+ (for script execution)
GPS receiver (for GPS sync)
Administrator privileges (for time synchronization)

Installation & Launch

Using the exe (Recommended)

Place ChronoGPS.exe and icon.ico in the same folder
Double-click ChronoGPS.exe to launch (starts in Monitor-Only mode)
If time sync is needed, click the banner at the top to elevate

For automatic elevated startup at logon, see FAQ Q21.

Running from source

python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install -r requirements.txt
python main.py

How to Build the exe (for developers)

ChronoGPS is designed to be built inside a venv (virtual environment).
Running PyInstaller in a global Python environment is not recommended,
as it may cause dependency contamination and reduce build reproducibility.

1. Create and activate a virtual environment (Windows / PowerShell)

python -m venv .venv
.\.venv\Scripts\Activate.ps1

2. Install dependencies

pip install -r requirements.txt
pip install -r requirements-dev.txt
pip install -U pyinstaller

3. Run tests (required)

python -m pytest -q

Make sure all tests pass before building the executable.

4. Build the exe (clean build)

pyinstaller --noconfirm --clean --onefile --windowed `
  --name "ChronoGPS" `
  --icon ".\icon.ico" `
  --add-data ".\icon.ico;." `
  --add-data ".\icon.png;." `
  --add-data ".\donate_qr.png;." `
  --add-data ".\locales.py;." `
  --add-data ".\locales_override.py;." `
  --add-data ".\gps_time_sync_config.json;." `
  --hidden-import "tkinter" `
  --hidden-import "tkinter.ttk" `
  --hidden-import "tkinter.messagebox" `
  --hidden-import "tkinter.filedialog" `
  --hidden-import "tkinter.scrolledtext" `
  --hidden-import "admin" `
  --hidden-import "startup" `
  --hidden-import "shutdown_manager" `
  --collect-submodules "tkinter" `
  .\main.py

Build policy

Always use --clean to prevent contamination from previous build/dist artifacts
Since v2.5, admin / startup / shutdown_manager are explicitly listed under --hidden-import
Only explicitly include required files — never bundle the entire project directory

After the build completes, ChronoGPS.exe will be created in the dist directory.

5. About icons

The exe file uses the ChronoGPS application icon
The tray icon intentionally uses a clock icon for better visibility
(to avoid loss of contrast at small tray icon sizes)

Quick Start

Connect a GNSS receiver to your PC (USB GPS receiver recommended)
Launch ChronoGPS.exe — it starts in Monitor-Only mode by default
Click the banner "Enable Time Sync (Restart as Administrator)" to enable sync
Select the COM port and baud rate (default: 9600), then click Start
Click Sync GPS or enable Instant Sync — ChronoGPS will reference GNSS continuously

If your COM port does not appear in the list, you can type it manually (e.g. COM16).
For NTP-only use, skip steps 1 and 4 — enter an NTP server and click Sync NTP.

Usage

GPS Sync

Connect your GPS receiver to the PC
Select the COM port and baud rate (usually 9600)
Click Start to begin receiving
Set GPS sync mode to Instant or Scheduled

GNSS Sync Recommendation

ChronoGPS uses GNSS (GPS, QZSS, etc.) as an absolute UTC time source.

For everyday FT8 / FT4 operation, Instant Sync is recommended.

Instant Sync is designed to:

Calibrate the Windows system clock using GNSS
Then monitor the offset while respecting the OS time model
Apply only minimal, necessary, and explainable corrections when needed

The key point is that Instant Sync does not mean "rewrite the system time every second."

Note

What "Instant Sync is usually sufficient" means

It means you do not need to repeatedly force clock rewrites once the system clock has been properly calibrated.

It does not mean you should turn synchronization off afterward. Keeping Instant Sync enabled during operation is perfectly fine.

Instant Sync continuously references GNSS, but corrections are applied only when necessary.

It also does not mean GPS reception should be stopped. GPS reception may continue for monitoring, visualization, and verification purposes without any issue.

Interval Sync (Weak Sync) is intended for:

Monitoring clock drift during long sessions
Verifying GNSS reception stability
Diagnostics and verification

For a deeper explanation of the design philosophy — including why Instant Sync works well for FT8/FT4, how Weak Sync behaves, and how ChronoGPS avoids injecting GNSS jitter into the OS clock — please see the FAQ:

👉 FAQ (English)

Weak Sync (Interval) Behavior

Weak Sync (Interval) is primarily intended for monitoring.
When the offset remains within the threshold, no correction is applied by design.

Interval (Weak Sync) follows the model:
"collect samples every second → evaluate only when the interval is reached."
If the offset is within the threshold, the system clock is intentionally not adjusted,
preventing GNSS reception jitter from being injected while still monitoring drift.

Interval Sync is not designed for continuous clock correction.
For real-world FT8 / FT4 operation, Instant Sync is strongly recommended.

How it works

ChronoGPS continuously collects GNSS time offset samples every second (without modifying the OS clock)
When the configured interval is reached, the accumulated samples are evaluated to decide whether a correction is necessary
If the median offset is within the threshold, ChronoGPS intentionally skips applying SetSystemTime to avoid injecting GNSS reception jitter into Windows

Gradual one-direction drift (this is normal)

You may observe a gradual one-direction drift in the log, such as -0.03s → -0.05s.

In most cases, this represents the natural drift of the PC's system clock, not a synchronization error.
As long as the offset remains within the threshold, ChronoGPS will deliberately not correct it.

Default weak-sync parameters

Threshold: ±0.2 seconds
Sample window: median of the last 30 seconds

NTP Sync

Enter an NTP server (default: pool.ntp.org)
- Recommended for Japan: ntp.nict.jp
Click NTP Sync for immediate sync, or enable auto-sync

Note

Using GPS Sync and NTP Auto-Sync simultaneously

If GPS sync is active and NTP auto-sync is also enabled,
the two sources may repeatedly correct each other in a "ping-pong" effect,
resulting in unstable time accuracy.

When GPS reception is stable, it is recommended to turn off NTP auto-sync
Use NTP as a backup when GPS is unavailable, or for manual one-time sync
The NTP Sync button (manual) is always available regardless of the auto-sync setting

FT8 Offset

If your FT8 timing is slightly off, enter an offset value (seconds) and click Apply.
Quick ±0.1s adjustment buttons are also available.

About Displayed Time Differences

You may occasionally see small differences between the displayed
System Time, GPS Time, and NTP Time.

These differences are caused by update timing and display refresh intervals.
They do not indicate an error in actual time synchronization.

The internal synchronization logic maintains millisecond-level accuracy.

About Satellite Information

Display	Meaning
In Use (GNSS)	GPS / GLONASS / BeiDou / Galileo primary satellites — used directly for time and position
In Use (SBAS)	WAAS / MSAS / EGNOS augmentation satellites — used for correction, not as a time source
Tracked	Received but not used in the time/position solution

SBAS satellites (MSAS in Japan) may be tracked but not appear as In Use — this is normal behavior.
SBAS provides augmentation corrections, not a primary clock signal.

ChronoGPS uses GNSS primary satellites and NTP for time synchronization,
a design comparable to professional GNSS timing receivers.

QZSS (Quasi-Zenith Satellite System / Michibiki) will appear in the satellite view tab if supported by the receiver.
Some receivers disable QZSS NMEA output by default — an empty QZSS panel is normal behavior.

Notes

Starting with v2.5, the UAC dialog at launch has been removed. ChronoGPS starts in Monitor-Only mode by default
To enable time sync, click the banner at the top of the window to elevate
The × button minimizes to the system tray. To fully exit, right-click the tray icon → Quit
Default NTP server is pool.ntp.org (can be changed to any preferred server)

File Structure

ChronoGPS/
├── README.md
├── README.en.md
├── docs/
│   ├── FAQ.md
│   ├── FAQ.en.md
│   ├── weak-sync-diagram.en.png
│   └── weak-sync-diagram.ja2.png
├── main.py               # Entry point
├── gui.py                # Main GUI
├── startup.py            # Argument parsing, mode selection, Mutex management (v2.5)
├── admin.py              # Admin check, UAC elevation (v2.5)
├── shutdown_manager.py   # Shutdown sequence management (v2.5)
├── config.py             # Settings (JSON)
├── locales.py            # Localization
├── locales_override.py   # Localization overrides
├── nmea_parser.py        # NMEA parser
├── ntp_client.py         # NTP client
├── time_sync.py          # Time synchronization
├── autostart.py          # Auto-start management
├── tray_icon.py          # System tray
├── requirements.txt      # Dependencies
├── icon.png              # App icon (PNG)
├── icon.ico              # App icon (ICO)
└── gps_time_sync_config.json  # Config file (auto-generated)

Download

Official binaries are distributed via GitHub Releases. Always check the "Latest" release.

Latest release: https://github.com/jp1lrt/ChronoGPS/releases/latest
ChronoGPS.exe — Windows executable
icon.ico — Application icon

Included files:

ChronoGPS.exe — Windows executable (PyInstaller build)
icon.ico — Application icon
checksums.txt — SHA256 checksums for release files

Verify downloaded binary (PowerShell):

Get-FileHash .\ChronoGPS.exe -Algorithm SHA256

Compare the printed hash with the corresponding line in checksums.txt attached to the release.

Security Notes

Always download from the official GitHub Releases page (link above). Avoid unofficial sites or third-party distributions.
All releases include a GPG signature (checksums.txt.asc). Note that Windows Authenticode signing (which suppresses SmartScreen warnings) is not currently implemented.
VirusTotal scan results are published with each release for transparency.

Third-party bundling / redistribution policy

If you bundle ChronoGPS with another application or installer, please use the official binaries from GitHub Releases (the exact files covered by checksums.txt).
If a rebuild is unavoidable, please publish a clear build identifier and SHA256 hashes for the distributed artifacts. (Same version number + different binary makes verification and support difficult.)
Please do not modify and redistribute binaries in a way that could be mistaken for an official release.

Support boundary

Issues reproducible with the official release are welcome in this repository.
Issues specific to a third-party bundle/launcher/installer (packaging, permissions, config location, update behavior, etc.) should be handled by the bundling project first.

False Positive Warnings from Antivirus Software

Some antivirus software may flag ChronoGPS.exe as suspicious. This is a known false positive caused by heuristic detection of PyInstaller-built executables. The application contains no malicious code.

All source code is publicly available and you can build the exe yourself.

VirusTotal scan results (v2.5.3): https://www.virustotal.com/gui/file/4955b362af0535a8baea7d6b592405a760bf96948ae7802ca551ed87ca530f5a/detection
(3/72 detections — Arctic Wolf / Bkav Pro / SecureAge — all heuristic false positives)
This has been reported to Microsoft as an incorrect detection

English — Verify downloaded release files

Import the maintainer's public key from GitHub:

# Linux / macOS
curl -s https://github.com/jp1lrt.gpg | gpg --import

# Windows (PowerShell)
Invoke-WebRequest -Uri https://github.com/jp1lrt.gpg -OutFile mypubkey.asc
gpg --import mypubkey.asc

Verify the detached signature on checksums.txt:
```
gpg --verify checksums.txt.asc checksums.txt
```
You should see a "Good signature". Confirm the key ID and UID:
- Key ID: 864FA6445EE4D4E3
- UID: Yoshiharu Tsukuura <jp1lrt@jarl.com>
Compute the SHA256 of the downloaded asset and compare with checksums.txt:
```
# Windows PowerShell
Get-FileHash ChronoGPS.exe -Algorithm SHA256

# Linux / macOS
sha256sum ChronoGPS.exe
```
Ensure the printed hash exactly matches the corresponding line in checksums.txt.
If the signature is invalid or the key/UID differs, do NOT trust the files and contact the project maintainer.

License

See LICENSE for details.

Author

Yoshiharu Tsukuura / 津久浦慶治
Amateur Radio Station JP1LRT

QRZ.com: https://www.qrz.com/db/JP1LRT
GitHub: https://github.com/jp1lrt

Donate

If you find ChronoGPS useful, a small donation would be greatly appreciated
and help support future development ☕

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File metadata and controls

ChronoGPS

Design Philosophy

Typical Use Cases

Why ChronoGPS?

Features

Screenshots

Operation Modes (v2.5+)

At Launch (Default: Monitor-Only)

When You Need Time Sync

Command-Line Launch

Requirements

Installation & Launch

Using the exe (Recommended)

Running from source

How to Build the exe (for developers)

1. Create and activate a virtual environment (Windows / PowerShell)

2. Install dependencies

3. Run tests (required)

4. Build the exe (clean build)

5. About icons

Quick Start

Usage

GPS Sync

GNSS Sync Recommendation

Weak Sync (Interval) Behavior

How it works

Gradual one-direction drift (this is normal)

Default weak-sync parameters

NTP Sync

FT8 Offset

About Displayed Time Differences

About Satellite Information

Notes

File Structure

Download

Security Notes

Third-party bundling / redistribution policy

Support boundary

False Positive Warnings from Antivirus Software

English — Verify downloaded release files

License

Author

Donate