Hi Ten seconds a month is "wrist watch" accuracy at constant temperature. For $3 Maxim will sell you a +/- 2 ppm real time clock. That will hold your 1 second for 500,000 sec (5.787 days). A cheap cell phone style TCXO at $1 or so should hold < 1 ppm over a modest range. That will get you out to > 10 days.
A lot depends on how stable and repeatable your environment is. Most indoor areas cycle up and down, but they repeat the cycle. What happens this week is a lot like what happened a week ago. If you can take a time reading every few days, you likely can do some smarts to extend the holdover quite a bit. With a modern low power CPU, the smarts will pull a lot less current than your real time clock or your TCXO. Yup, this is all basement engineering. If somebody's life depends on it, maybe not such a good idea. Bob On Nov 20, 2012, at 10:46 AM, Chris Albertson <albertson.ch...@gmail.com> wrote: > I don't think GPS is ever so in accurate as to have a 1 second error. If > it has a solution at all it is going to be at least within a millisecond. > > The way "everyone" handles "holdover" (Holdover is timekeeping with GPS is > not available) is to keep a local clock driven off a stable oscillator. > Then when you do have GPS you adjust the clock. Then when GPS goes away > you "free wheel". > > With your very loose one second requirements you can use a rather > inexpensive clock, perhaps just a TCXO. The question is how long of a > hold over period must you be able to handle. If GPS will is unavailable > for a month then you will need a VERY good clock but if you will only loose > GPS for a few hours at most it can be cheaper. > > Active antenna are not a perfect solution. What the GPS needs is good > signal to noise and the amplifier amplifies noise as well as signal. It > can help in some cases and is worth doing if you have the space and power > budget. > > So to design this step one is to select an oscillator that has the required > stability for "one second error durring the worst case holdover period" thn > build a clock based on that. Next design a way to re-set the clock based > on GPS. > > > On Tue, Nov 20, 2012 at 3:33 AM, Tom Harris <celephi...@gmail.com> wrote: > >> Greetings >> >> I know that the accuracy of GPS degrades indoors. However, suppose >> that I just want to turn a GPS module on, acquire the current time >> accurate to a second, and then turn it off. I can get a good deal on >> the U-Blox LEA-5H modules (same as used on Arduino shields I think), >> which have a high sensitivity, and I can use an active antenna if >> needed. >> >> Am I wasting my time. Sorry for not requiring the time more accurate >> than a second, but that's all the clients require. >> >> -- >> >> Tom Harris <celephi...@gmail.com> >> >> _______________________________________________ >> 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 > 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.
