[time-nuts] Discipline an oscillator with NTP?

paul swed paulswedb at gmail.com
Sat Jul 23 19:19:42 UTC 2011


Indeed thats why I was saying choose 3 servers.
Now I see in the thread that you can pick pools of servers so thats good.
Then average what they say the time is and drive oscillator.
Wonder if you could look towards the stratum 1 servers.
But that said I could easily believe that it might ot be any better then
wwv.
Good thread. Things to learn as we all seek a backup to GPS I assume.
Regards
Paul
WB8TSL

On Sat, Jul 23, 2011 at 2:17 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> WWV "as transmitted" is massively more accurate than it is as received.
> There are a lot of NTP servers out there with offsets in the ms to fraction
> of a ms range. Even if your path was perfect, those issues would keep you
> from getting to the us level. You could indeed build up some custom servers
> and take care of the issue. At least  as I understood the original question,
> random servers on the net were the time source. I assume you would pick them
> for short path to your location, and then reject any that did really stupid
> stuff.
>
> Bob
>
> On Jul 23, 2011, at 2:02 PM, Chris Albertson wrote:
>
> > On Sat, Jul 23, 2011 at 10:40 AM, Bob Camp <lists at rtty.us> wrote:
> >
> >> There's also the basic "do I trust the server" issue. You can indeed
> trust WWV as transmitted.
> >
> > NTP's clock selection algorithm is pretty good.  If you choose a
> > diverse set of servers then NTP will only use the subset of them that
> > are self consistent.  "Pool" servers are assigned randomly so even if
> > there were many bad servers in the world the chance of randomly
> > picking five that were are "bad" in the exact same way is about zero.
> > Typically when a server has a problem it does not match another
> > randomly selected ntp server.
> >
> > So I think you can trust the consensus time from a set of five
> > randomly selected pool servers.  It would be far easier to spoof WWV,
> > just set up a transmitter.
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> >
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