Musings on PC Clock Accuracy

As a digital mode and satellite operator, accurate time is essential.  The internet is a wonderful step forward in that Network Time Protocol (NTP) services give the potential for every PC to be accurate to within milliseconds.  Windows recognizes this and has a service called W32tm that deals with clock settings using NTP.  Unfortunately most of the interesting settings are buried in the registry, such as the polling interval which is set to check the time about every 9 hours.  Also the default NTP servers often do not work (for me at least), and I’ve found the servers to be far more robust.   There is a nice post that describes these details at Windows Central.

There are several very sophisticated time services such as Dimension4 or Meinberg that can be installed on a PC.  The installation and configuration is non-trivial, however.  And of course that is “one more thing” to worry about in terms of security.  Personally I’ve found it far easier to add the servers and change the HKEY_LOCAL_MACHINE\SYSTEM\ControlSet\Services\W32Time\TimeProviders\NtpClient   SpecialPollInterval  Registry key entry to something more like an hour (3600 seconds).

This time (no pun intended) that didn’t work for me.  Every time my new shack PC boots up, it dutifully uses NTP services and manages to set the PC clock to a value that is consistently 0.4 seconds behind.  I suspect during the boot process, some higher priority task is managing to interfere between obtaining the correct time, and setting the PC hardware clock.  To make matters worse, manually requesting windows to adjust the time automatically doesn’t work either.

There are two work-arounds.  The first is simply waiting for an hour (the SpecialPollInterval).  At that time windows will synch up and remain accurate, never being off more that a few milliseconds.  The second is to turn off automatic time adjustment, adjust the clock by a minute or two manually, then turn automatic time adjustment back on.  I’m guessing that windows has some sort of feature that prevents it from constantly messing with the clock until some threshold difference between NTP time and PC Hardware Clock time has been reached.

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One Response to Musings on PC Clock Accuracy

  1. Dick, K1HC says:

    Very much agree on the issues with trying to use Meinberg and Dimension4! I gave up on them, and I went to a small GPS receiver, the GlobalSat BU-353S4 which sells for about $30 on eBay and the NMEATime2 software which you can download for about$20. Amazingly, that little GPS “hockey puck” just sitting in my basement window (facing north) acquired several GPS satellites in a few moments and has been perfect for keeping my times exact for MSK144 and FT8. Those who operate portable would find this set up very useful as well. I found a great article by Gene Hinkle, K5PA, on how to go about setting it up – just Google it. 73 from Dick, K1HC

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