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

Dave Baxter spam at goes.nowhere.com
Thu Dec 3 11:38:14 UTC 2009


In article <2K9Rm.10560$Ym4.4851 at text.news.virginmedia.com>, david-
taylor at blueyonder.not-this-bit.nor-this-part.co.uk.invalid says...
> 

> Keep asking the questions, even if they seem elementary - and I will
> try to both provide answers and record them on my Web site for others. 
> One issue which you haven't addressed (as far as I know) is how the 
> Faros program uses an accurate time.  I take it that the author of the 
> program gets the time from Windows - he does know that time is 
> typically only updated once every ten milliseconds, I guess?
> NTP doesn't have an API which can tell you the time more accurately
> than that, which is a pity because that would be very handy....
>
> 73,
> David 

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.




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