From: Hal Murray
david-tay...@blueyonder.co.uk said:
You can use a GPS puck or equivalent with PPS output to get the sort of
accuracy you need. ..:
PPS output is only half the battle. You also have to get it into the system
that needs it.
A modem control signal on an old fashioned serial port (not USB) is the
classic approach. Unfortunately, many modern systems, especially laptops,
don't have serial ports.
GPIO pins on things like a Raspberry Pi also work well.
PPS over USB adds the USB polling interval to the error budget. It will
probably work well enough if the goal is under 15 ms.
====================
Hal,
Agreed, PPS over USB isn't ideal, but possibly the extra jitter in the
context of a Windows system isn't too bad. On desktop systems I've been
able to add a 3rd-party serial PCIe card and get excellent results.
On laptops I've usually been able to get well under a millisecond over
Wi-Fi:
http://www.satsignal.eu/mrtg/performance_ntp.php#wifi
apart from one rather cheap-and-nasty system which I won as a prize. I
wonder why they were giving that unit away!! The secret is, perhaps, the
new API introduced in Windows-8 (with some pushing from Dave Hart, I
suspect) which allows much more precise retrieval of the Windows time, and
is used by NTP when possible.
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv
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