It could be possible to use two Rb GPSDOs, one providing the PPS and another disciplined by GPS, then rotate them every month.
On Fri, Dec 28, 2012 at 2:41 AM, Attila Kinali <[email protected]> wrote: > On Thu, 27 Dec 2012 10:19:46 -0800 > Chris Albertson <[email protected]> wrote: > >> Yes you could us something like one of the low-cost rubidium >> oscilators to supply a pulse per second to Linux NTP and it would work >> for some time before the error was as large as 10 mS. >> >> One missing requirement is how long you need be without GPS or >> networking. Obviously you can't stay out of contact with the world >> forever but it is very easy and cheap if you only need a day. Harder >> if you need a month and expensive if you are talking about years. > > Actually, a couple of months is still quite simple. > The Rb approace gives you at least something in the range of 10^-9 stability, > long term. Which gets you into the ballpark of 100 days (with 10ms). If you > temperature stabilize the Rb you should get down to 10^-11, which would > be 30 years. At least theoretically, aging is AFAIK larger than this. > But a couple of years should be still possible without too much effort. > > IIRC the FE5680 sell now for 200USD. Some heatsink and temperature control > come maybe at 50-100USD. Some equipment to measure where the PPS lies > relative to UTC and a powersupply that can get you 15V from mains and > a battery (to get the Rb where the computer is) would also be necessary. > > Alternatively, put the Rb next to the computer in question, hook a powerfull > linedriver to the PPS output, and a wire that goes all the way out where > you have GPS reception and can measure the PPS pulse. After measurement, > you can remove that cable. > Ofcourse this only works, if you can lay a cable temporarily. If you are in a > EMP secured room, the only way to get the pulse measured is the approach > with the traveling Rb. > > Attila Kinali > > -- > There is no secret ingredient > -- Po, Kung Fu Panda > > _______________________________________________ > 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.
