[ntp:questions] help with setting up NTP on windows with a USB GPS

David J Taylor david-taylor at blueyonder.not-this-bit.nor-this-part.co.uk.invalid
Thu Dec 3 14:22:48 UTC 2009

"Dave Baxter" <spam at goes.nowhere.com> wrote in message 
news:MPG.2581b3818527b329989695 at news.btopenworld.com...
> Hi..
> Back after getting diverted by my central heating system going on the
> blink...
> Re Faros.  Good question, well presented, unknown (exactly) at this
> time!
> It does run it's own internal software clock, that I do know having
> asked Alex (VE3NEA) questions about it in the past.   That in turn is
> synched to a reference by NTP (not SNTP) it does not (AFIK) use
> "Windows" time in any way.
> (Sadly, he's totally uninterested in making it able to use a local GPS
> receiver with PPS, or a radio time code RX.)
> It's own internal timekeeping routines use a Kalman Filter (Think that's
> what it's called) to determine "true" time from a number of NTP sources.
> It is also quite "chatty" I expect compared to a true NTP client, as it
> will poll the NTP server (or selected collection of servers in rotation)
> about every 10 seconds!  Another reason I think a local server would be
> best :-)
> Generally it keeps good time, to within a mS or so, as it can reliably
> tell if a received signal comes the short or long way round the globe,
> even from New Zealand!  (A close call that one though.)
> However, it (for whatever reason) is not good at handling variable
> network latency, especially if the flight times to/from the server are
> different, as seems to be the case at odd times of day at present.
> With the Meinberg NTP server in the path now, doing the synchronization
> to the outside world's NTP boxes (for now) things are a little better.
> At least, it takes longer for the variable latency problem to screw
> things up, but it also takes longer to recover too.   Extra "filtering"
> in the overall path I guess.  (Software algorithms etc in the Meinberg
> software.)
> Anyway.  After reading all the info here, I now think I know how to do
> it correctly, setting up the Meinberg program, and overlaying Dave Harts
> binaries on it, also doing the registry thing pointing at the PPS
> supporting serial driver, so when I get enough of the right sort of time
> next time, I'll try again.
> One thing I picked up on, is the parameters in the NTP config file,
> regarding poll times.  The units of measure are not mS, but 2^n mS, I
> think?
> By the time I get my head round all this, we'll have probably lost HF to
> PLT anyway.
> Regards to All.
> Dave Baxter.

Dave, quite a few points there!

Polling external NTP servers every ten seconds is /very/ unfriendly, and 
some servers are likely to return the kiss-of-death to such a client, and 
may also deliberately return you an incorrect time value.  Using a short 
poll against your own server on your own LAN is a different matter, of 

It sounds as if the best arrangement would be to have one PC as a 
stratum-1 NTP server (and it could be Windows- or FreeBSD-based), and get 
your Faros PC syncing to it.  Having that server on your LAN should 
greatly reduce the variable network latency.  You shouldn't need any extra 
filtering with a LAN poll time of 32 seconds (maxpoll 5).

I don't know Faros, but perhaps you could manage on a single PC by 
selecting the NTP server for Faros as - the localhost - and 
having that same PC as a stratum-1 server from the GPS/PPS arrangement we 
have discussed.  This would provide a GPS or radio-clock time source, but 
with some additional control and filtering.

Poll times in the ntpq -p display are in seconds, as are the "when" times. 
You should see the "when" increasing by one per second until it reaches 
(or just exceeds) the "poll" value.


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