If you’re looking to build a primary time server for any project, you might think to use a Raspberry Pi to serve your purpose. But where to begin? Yes that is an older Raspberry Pi Model B, but this epic 15K+ word write-up over at satsignal.eu is a great place to begin configuring your NTP server.
From graphs recording GPS signals in different temperature environments and locations to configuring and checking software settings in your setup, NTP is absolutely essential for clock synchronization across networks like the Internet. And this how-to will get you within a few milliseconds of your timekeeping needs.
As an experiment, I purchased one of the low-cost credit-card-size Raspberry Pi computers, and have configured it to run NTP (Network Time Protocol). I have also used this board with a GPS receiver with pulse per second (PPS) output to make a stratum-1 NTP server, but as I know little of Linux, it has taken some time to achieve this aim! There are some helpful Linux commands scattered throughout this page. These notes are almost as much for my own records for the next time I need to visit this project, but I hope they may be helpful to others.
I start by describing how to get the Raspberry Pi running with just a LAN connection – no display, keyboard or mouse – a so-called headless operation. I then describe how to configure NTP for your environment, and adding a GPS/PPS receiver to convert your box into a stratum-1 NTP server including the operating system updates needed. Next, I note a couple of problems I had with the first GPS receiver I tried, and how I cured those with a different GPS receiver to produce a stratum-1 NTP server consuming about 4 watts.
Note that good performance is dependant on the GPS unit having a clear view of the sky, particularly the southern part of the sky if you are in the northern hemisphere. With older GPS receivers this required an outdoor antenna, but more modern units such as those mentioned here may well work indoors providing that some sky is visible, perhaps on the top floor of the building (as I am). If you have an “RF-proof” roof (lead-lined, perhaps?!) or certain windows with a lining to stop incoming heat, or wall construction including metal, you may still need an outdoor antenna, and almost certainly if you live in a basement! Whilst weather will normally have only a small effect in the signal – e.g. heavy rain – it’s possible that a layer of snow could attenuate the signal enough to stop the GPS receiving enough signal. Monitoring performance may help you spot these problems. (Thanks to Joe, HB9DRT for the information on snow – I’ve only seen that problem once here during an exceptionally cold winter).
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