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 <[email protected]> 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 <[email protected]> wrote: > > > [email protected] 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. > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] -- To unsubscribe > send > > an email to [email protected] > > To unsubscribe, go to and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
