[time-nuts] Re: NTP servers

[Avamander]

Speaking of Raspberry Pi's as time servers, does anyone here know of a nice
single board computer that supports both Ethernet hardware timestamping and
GPIO PPS input?

On Tue, Nov 23, 2021 at 12:49 PM McFail Troll <time.isanapp at gmail.com>
wrote:

> > If you have a good local NTP setup, you can measure how good other
> servers are, or more likely how good the network connection is.  NTP
> assumes the network delays are symmetric.  Often, that's not true.  So "how
> good" turns into measuring network (a)symmetries.
>
> Yes this is what I'd like to do eventually. Trying to get a Raspberry pi +
> gps setup going first though.
>
> On Mon, Nov 22, 2021 at 5:42 AM Hal Murray <halmurray at sonic.net> wrote:
>
> > time.isanapp at gmail.com said:
> > > but I am curious to see if I could sync up with some of you guys who
> > seem to
> > > have some pretty cool set-ups.
> >
> > GPS has taken over the time-distribution business.
> >
> > If you want to use GPS, there are 2 ways to go.
> >
> > You can get a simple GPS receiver and plug that into your PC.  For decent
> > time, you need a PPS signal and a real serial port, not USB.
> >
> > The other approach is to get a GPSDO -- GPS Disciplined Oscillator.
> > That's a
> > box with a GPS receiver and a good crystal and some software.  It
> smoothes
> > out
> > the rough edges in the timing from the GPS signal and/or keeps going
> > (holdover) when the GPS signal fades or dies.
> >
> > GPS is very very good in the long term but noisy in the short term.
> Short
> > means seconds to minutes.  Long means days/months.  A GPSDO will get rid
> > of
> > most of the short term noise.
> >
> > There are/were several models available at relatively low cost after they
> > were recycled from cell phone towers.  HP Z3801A and Trimble Thunderbolt
> > are popular.  "GPSDO" will get lots of hits on eBay.  I don't know how
> good
> > the recent ones are.
> >
> > Just reading the info available can be fun if you like that stuff.
> >   http://www.realhamradio.com/GPS_Frequency_Standard.htm
> > The Z3801A manual is a good read.
> >   http://www.leapsecond.com/museum/z3801a/097-z3801-01-iss-1.pdf
> > Time sink warning!
> >
> > GPS works much better if you have a good antenna location.  Modern GPS
> > receivers are sensitive enough that they sometimes/often work indoors,
> > maybe better on a window sill, maybe even better if the window faces
> > south.  Just because it's working now doesn't mean it won't glitch often
> > enough to cause problems.  Mumble.  Try it and see what happens.
> >
> > ---------
> >
> > There is actually a 3rd way: buy a box that does it all.  But that's not
> > much
> > fun, at least for most of the people on this list.
> >
> > ----------
> >
> > > there are plenty of good stratum 1 NTP servers open to the public (e.g.
> > > NIST's servers),
> >
> > If you have a good local NTP setup, you can measure how good other
> servers
> > are, or more likely how good the network connection is.  NTP assumes the
> > network delays are symmetric.  Often, that's not true.  So "how good"
> turns
> > into measuring network (a)symmetries.
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
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