Someone at my radio club uses some mode of operation where accurate
time is required. He said the standard Windoze clock does not keep
sufficiently accurate, so he has software which updates from an NTP
server every 4 seconds or so. It's not exactly a denial of service
(DOS) attack, but seems almost close to it in NTP terms to me. I can't
really believe updating every few seconds is sensible myself, but he
assures me it works very well. (I'm rather hoping it does not use a
stratum 1 server!)
I'm sure someone will say if you want accurate time on a PC, to use
some combination of GPS, rubidium or OCXO with a 1 pps pulse and a
serial port on a FreeBSD or similar computer. But that's probably not
practical if your software only works on Windoze.
Any comments?
Dave, G8WRB.
======================================
Dave,
I very much doubt that with a typical consumer-level Internet source you are
going to do much better than a millisecond over the day, as the load can
vary so much (and hence the packet delay time), and some ISPs don't
prioritise NTP packets in any case (they may prioritise other traffic
instead).
For the millisecond level of accuracy using Windows I would strongly
recommend a local clock with a GPS/PPS source. It is entirely practical on
Windows:
http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html
http://www.satsignal.eu/ntp/Sure-GPS.htm
I've used such sources on Windows 2000, XP and Windows-7 and you can see the
accuracy obtained here:
http://www.satsignal.eu/mrtg/performance_ntp.php
The Windows 2000 box does seem very sensitive to higher CPU use causing an
internal temperature drift and hence millisecond errors.
I've also made a simple NTP server using the low-cost Raspberry Pi board and
GPS/PPS which gets "microsecond" level offsets, and you could hard-lock a
Windows PC over the LAN to such a server using short polling intervals such
as you suggest. PCs Hydra and Narvik in the above graphs are LAN-connected
with a 32 second polling interval to local stratum-1 servers. Other
non-stratum-1 PCs are Wi-Fi connected.
Note that Windows-8 has a new high-precision GetSystemTime call which may be
helpful to those writing such programs.
If, as others have suggested, only fractions of seconds are needed, then a
well-configured NTP (not the so-called Atomic Time programs), may well
suffice. I have install details for NTP on my Web site:
http://www.satsignal.eu/ntp/setup.html
73
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
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