Using NTP
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Accurate Time Keeping on your PC using NTP

An important part of any satellite reception operations is accurate time keeping.  This is particularly important for receiving High Resolution Picture Transmission (HRPT) data where an antenna must be kept pointing at a satellite that is tracking rapidly across the sky, but it is also important for automated operations where the accuracy of a geographic overlay on the image may rely on knowing exactly when that image was received.

Running on many Internet servers is the Network Time Protocol (NTP) which allows hierarchical synchronisation of a network of machines to one common reference.  Accuracies down to milliseconds are easily achievable.  With some of the software you can also use an alternative reference source such as a GPS or Radio Clock receiver.  I have used a Garmin GPS18 LVC GPS puck which has both a serial and pulse-per-second output as a reference clock on both a FreeBSD and Linux, with a variety of Windows systems.  It's a fun project, and your PC time will likely be accurate better than a few hundred microseconds!

I have a permanent connection

I use Windows XP/Vista/7/8/10

Personally, I now recommend the Meinberg NTP Windows port, and there are extensive notes on installing should you need them.  NTP runs as a service on Windows, meaning that it starts with Windows and requires no user intervention and continues to work whether the user is logged in or not.  When the time error is small (less than 128 milliseconds) the software works in a fine frequency change mode, rather than crudely stepping the clock to a new value.  NTP software is available for a wide number of machine types (not just Windows).  You can download various versions including Apple, UNIX etc. from:

Please note that you may need to set the W32Time service (Windows Time) to disabled to stop it interfering with the operation of NTP - this is done automatically by the Meinberg installer.  If you want to see the accuracies I get one my system, please see my timekeeping accuracy data, which is updated every 30 minutes.  Be aware that because of the plotting software I use, an offset is added to the values (the software can't plot negative values) so that values plotted at the middle of the graph actually mean zero offset.  Please note that the scales on the various graphs are different, as the PCs have differing sync sources and capabilities.

I use Windows 95/98/ME/NT/2000

It's well past time to upgrade!

I have a dial-up connection

Use the NTP software mentioned above, which now detects when a new connection is established.

How accurate is NTP?

Please see my NTP Monitoring data (updated every 15 minutes).


Software which is no longer recommended (because NTP is so good!)

Historically, when I used dial-up, I used Tardis, and was very happy with it:

This software will work on all versions of Windows.  Please note that this is shareware.  The unregistered version is fully functional, although you should support the author by registering if you continue using this software.  

If you simply want to sync your computer to its own CMOS Time Of Year (TOY) clock, Geoff Whitbourn recommends ClockMon (  This program addresses a slightly different issue, that of lost interrupts causing the OS time to become out-of-step with real time.

Copyright © David Taylor, Edinburgh   Last modified: 2016 Jun 03 at 08:49