Even something as simple as a Chronodot will hold to a few seconds a year. Make something out of an ocxo and you can beat that. You just need to transfer time in from some outside source once a year or so to synchronize it. Make your gizmo output GPS time sentences and most NTP implementations should be able to read it.
On Fri, May 17, 2013 at 9:52 AM, Bob Camp <[email protected]> wrote: > Hi > > I believe the original spec on this was "accurate to a few seconds". If > that's still the case (I have been known to miss zigs and zags in threads > …) the sync requirement isn't terribly stringent. A wrist watch and some > care can get you to a fraction of a second. > > Bob > > On May 17, 2013, at 12:31 PM, Mark Spencer <[email protected]> wrote: > > > Hi. > > > > Re the setting issue I'd look for a solution that can be initially > synchronized from the 1pps pulse from a GPS receiver or other precision > source. > > > > If you search for prior posts from me over the last several weeks you > should be able to find one where I expand on this in a bit more detail. > (Sorry I am on the road right now.) > > > > Regards > > Mark Spencer > > > > --- On Fri, 5/17/13, [email protected] < > [email protected]> wrote: > > > > > > From: [email protected] <[email protected]> > > Subject: time-nuts Digest, Vol 106, Issue 80 > > To: [email protected] > > Received: Friday, May 17, 2013, 9:00 AM > > > > > > Send time-nuts mailing list submissions to > > [email protected] > > > > To subscribe or unsubscribe via the World Wide Web, visit > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > or, via email, send a message with subject or body 'help' to > > [email protected] > > > > You can reach the person managing the list at > > [email protected] > > > > When replying, please edit your Subject line so it is more specific > > than "Re: Contents of time-nuts digest..." > > > > > > Today's Topics: > > > > 1. Re: Time source for indoor standalone PC (Chris Albertson) > > > > > > ---------------------------------------------------------------------- > > > > Message: 1 > > Date: Fri, 17 May 2013 08:43:07 -0700 > > From: Chris Albertson <[email protected]> > > To: Discussion of precise time and frequency measurement > > <[email protected]> > > Subject: Re: [time-nuts] Time source for indoor standalone PC > > Message-ID: > > <CABbxVHs9LaeJsuP8OXspVmzi+VfHHPUbeCBwAsZgBB+BK=f...@mail.gmail.com> > > Content-Type: text/plain; charset=ISO-8859-1 > > > > If there is no way to get radio signal into the room, then buy a rubidium > > oscillator. Conect the Rb to a small notebook PC the run Linux or BSD > > Unix. Let the Rb oscillator drive NTP and get it sync'd up outside your > > room and then walk the Rb/NTP server into the room. Because you are > > isolated you will need at least three of these systems and some people > > argue you need five of them. I'd argue five is certainly better, but > > three is a minimum. Then periodically you rotate one of the systems > > outside for calibration with GPS. > > > > Inside the room you configure the three to five servers to run in "Orphan > > Mode" This wil allow them to develop a kind of consensus time based ont > > the set of servers that agree. Hence the reason for having five servers. > > > > One real problem with a disconnected "island" is dectecting errors. How > to > > know if the server is 50 or so milliseconds "off". You can't depend on > > only one. > > > > The good news is theRubidium Oscilters are not expensive. $100 Will get > > you a working unit. And certainly PC notbook computers are dirt cheap if > > you buy older ones. > > > > The hard part here is setting the Rb units. They need to be GPS > > disciplined when GPS is available and then flip over to "hold over" mode > > when GPS goes away. with your low-precision requiremnts that should keep > > good time for over a year with GPS disconnected. Then you take them > > outside and run them for a few days with GPS. So with six servers, one > > would be outside and five inside and every two months you rotate them. > > This should let you run at the millisecond level and also have the > ability > > to withstand two server failures. > > > > > > > > > > On Thu, May 16, 2013 at 9:45 PM, Grant Waldram <[email protected]> > wrote: > > > >> Hi folks. I wouldn't call myself a time nut, so this is really an > effort to > >> ask for advice from some people who know the field. My first contact > with > >> time synchronisation was looking at the instrumentation clocks for the > >> Woomera rocket test facility when I went out there for a few (large!) > hobby > >> rocket launches. I can't even remember the system's name but it used a > >> series of pulses of various lengths to give a unique time code. But, I > >> digress... > >> > >> > >> > >> I've not had much need for time synchronisation over the years, but in > >> recent years NTP has been able to get me by. Unfortunately I'm now faced > >> with a network that needs a moderately correct clock (I'm scared of > using > >> the word 'acurate' around you folks!) to the order of a few seconds or > so, > >> but with no possibility of an external internet connection (for a > number of > >> reasons). At present I'm using one PC running Windows Server as an SNTP > >> server to synchronise all of the devices, as it is the only device in a > >> physically secure location. This is inside a security-fob protected > room. I > >> can't get GPS signals in there, and the Australian radio clock network > was > >> shut down about ten years ago. Our CDMA network was turned off in 2008. > >> Right now all I can think of is GSM, and while i know it's not terribly > >> accurate it seems like it might be the easiest. It also might be that > I've > >> got tunnel vision and there's a simpler solution out there. > >> > >> I would be quite happy with some sort of dedicated GSM/NTP-server box, > and > >> there are Arduino/Raspberry Pi/Linux homebuilts for that out there, but > I > >> have been wondering if one of the fairly common GSM USB sticks could > >> somehow > >> be a time source to set the server clock? > >> > >> > >> > >> Regards, > >> > >> > >> > >> Grant > >> > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > > > ------------------------------ > > > > _______________________________________________ > > time-nuts mailing list > > [email protected] > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > End of time-nuts Digest, Vol 106, Issue 80 > > ****************************************** > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
