GPS Time Sync

Synchronisation of the real time clock in your PC to the correct current time in your particular timezone can be critical for certain PC applications. For example, Amateur Radio operators using the WSJT-X application for weak signal digital communications all need to have their PC clocks set to within a few seconds of the correct time. Normally setting your PC clock is an automatic function of the operating system, requiring only an Internet connection. A smart device with access to a broadband network can provide an Internet connection via a WiFi hotspot. But what can you do in the absence of any Internet connection? Simply use this free GPS Time Sync application. It will synchronise your PC clock to the correct time using a GPS satellite receiver. How? The GPS receiver receives accurate time information from GPS satellites in order to determine its position. This GPS Time Sync application reads the time from the GPS receiver and uses it to set the PC clock.

GPS Time Sync Application

Requirements

You will need:

A working Internet connection to download the GPS Time Sync application.
A PC running Microsoft® Windows10™ or Windows11™
A GPS receiver connected to your PC via USB or a serial port

Installation

To get started: Request a link to our GPS Time Sync application here and follow these software installation instructions:

Download the GPStimesync.zip file using the link provided.
Go to your Downloads folder and right-click on the GPStimesync.zip file.
Select Extract All. A GPStimesync folder will be created.
Move the GPStimesync folder to a working folder of your choice. Note: You will need Administrator privileges to move it to the Program Files folder.
Open the GPStimesync folder and create a Windows shortcut to the GPStimesync.exe file if you wish.

Operation

Plug a USB GPS receiver into to a free USB port on your PC.
Orient the GPS receiver, typically outdoors, so that it has a clear view of the sky.
Observe the GPS receiver status LED:

It will flash once when first connected.
It will flash at a 1-second rate when GPS satellites are finally acquired. Reorient the receiver if it does not.

Double-click on the GPStimesync.exe application or shortcut.
The application will ask if you want to allow it to access your PC clock. Select Yes.
The application will search all available PC COM ports for the GPS receiver.
The GPS Status display will show:

"Searching" when looking for a PC COM port connected to a working GPS receiver.
"GPS found on <COM Port> at <Baud Rate> baud" Momentarily, when the GPS receiver COM port and baud rate are found.
"Not Connected" if the search could not find a working GPS receiver. It will then continue searching until one is found.
"No Fix" if a working GPS receiver was found, but it has not yet acquired any GPS satellites to get a time fix.
"2D Fix" if the receiver has acquired sufficient GPS satellites to get a basic time fix.
"3D Fix" if the receiver has acquired sufficient GPS satellites to get an accurate time fix.

The PC Time Offset display will show:

Nothing unless there is a 2D or 3D Fix
The offset in second, milliseconds or microseconds between the PC time and the GPS time. Negative means the PC is running slow.

The accuracy of the PC Time Offset is NOT GUARANTEED as there are many variables involved. The GPS Time Sync application only takes into consideration the expected transmission latency of the data from the GPS receiver, but it expects that:

The NEMA GPRMC message is transmitted by the GPS receiver immediately at the start of every second roll-over.
The data transmission occurs at full speed with 1 start bit, 8 data bits, 1 stop bits and no gaps.
The data transmission baud rate is accurate.
The PC immediately provides the data to the GPS Time Sync application when it is received.
The time offset is calculated and applied to the PC clock without any processing latency at all.

In reality, the observed offset between the GPS and PC clocks, when the data is received and updated, has a random discrepancy of up to several milliseconds. The GPS Time Sync application only applies PC clock updates that are considered to be more accurate than the previous updates. It begins again from scratch when the GPS fix is lost.
When the GPS Time Sync application indicates that it has applied a sufficiently accurate update (whatever you consider that is) it can be closed, as further updates are unlikely and the PC clock should remain stable for a considerable time.
Click on the button at the bottom of the GPS Time Sync application to open a browser and visit this page.