Accurate Time for Digital Modes by GPS

Accurate computer time is absolutely essential for successful QSOs using digital modes such as FT8, FT4 and JS8. While millisecond accuracy is not necessary, if the computer clock is off by more than a second, you are likely to experience problems. It is very easy to check the accuracy of your computer’s clock by using the website

A check of my computer’s clock on showed that it was 0.3 seconds behind. This is well within specs for digital modes.

Recent versions of Windows will frequently update the clock through time servers, but the updates are not usually as frequent or accurate as I would like. There are also several applications that will connect to Internet time servers to periodically update the computer clock. Some examples are Meinburg NTP, BktimeSynch, Dimension 4, and NetTime. I have Dimension 4 loaded on my shack computer.

Dimension 4 periodically updates the computer clock using a low level internet protocol, called SNTP, to connect with special purpose Internet Time Servers.

But what if you don’t have Internet access, due to an outage or working in the field? Fortunately, there are computer applications that will synchronize your clock using GPS signals. To do this, you need the software and a GPS receiver for the computer.

For my computer, I use a GlobalSat BU-353-S4 USB GPS Receiver and NMEATime2 software for GPS-PC time synchronization. The GPS receiver cost me $34, and it also cost me $20 to register the software.

The GPS receiver connects to a USB port on the computer as a serial device. I have the receiver in a windowsill near the computer.

On my computer, the GPS receiver is the Prolific USB-to-Serial Comm Port (COM4).

After the GPS receiver, I installed the NMEATime2 software. It was very easy to set up the software to work with the GPS receiver. Once installed, the software runs in the background to keep the computer clock updated. There is an icon in the system tray that shows the current status.

The green satellite icon in the system tray indicates that NMEATime2 has a good GPS signal lock and the application is disciplining the computer clock.

A right click on the tray icon and selecting “Show Panel” will bring up the software control panel with menus for settings and four tabs: Status, GPS Status, Loop Status, and NMEA Output. For my purposes, the Status panel and GPS Status panel contain the most important information.

The Status panel shows the current time and overall quality of the GPS satellite signals.
The GPS Status panel shows which GPS satellite signals are being received, and the signal quality for each, as well as location information.
The Loop Status tab displays the status of digital filters that filter out any spikes or outliers before sending the filtered signal to the application’s control algorithm.
The NMEA Output tab displays the NMEA data strings as they are received from the satellites.
While running NMEATime2, my computer time is usually exact or very close.