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 <mspencer12...@yahoo.ca> 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, time-nuts-requ...@febo.com <time-nuts-requ...@febo.com> > wrote: > > > From: time-nuts-requ...@febo.com <time-nuts-requ...@febo.com> > Subject: time-nuts Digest, Vol 106, Issue 80 > To: time-nuts@febo.com > Received: Friday, May 17, 2013, 9:00 AM > > > Send time-nuts mailing list submissions to > time-nuts@febo.com > > 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 > time-nuts-requ...@febo.com > > You can reach the person managing the list at > time-nuts-ow...@febo.com > > 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 <albertson.ch...@gmail.com> > To: Discussion of precise time and frequency measurement > <time-nuts@febo.com> > 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 <gr...@remobs.com.au> 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 -- time-nuts@febo.com >> 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 > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > End of time-nuts Digest, Vol 106, Issue 80 > ****************************************** > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.