Thanks to all who replied! It looks like the antioxidants will win and the clock will fail before the 100 years are up. Assuming the "accuracy" of the GPSDO is 1 part in 10^12 then the inaccuracy after 100 years will be up to : 60x60x24x365.25x100x1x10^-12= 3ms [approximately] - which is probably good enough for an old fella. I have to admit that I have an ulterior motive for asking this question : I wanted to know what sort of long term accuracy I could expect from the GPS constellation - looks as if 1 part in 10 to the 12th is about right. Cheers!...............................................................................Donald C.
On Sat, Jul 20, 2019 at 7:01 AM Bob kb8tq <[email protected]> wrote: > Hi > > The simple answer is that your clock is locked directly to a set of time > sources built > into the GPS satellites. Those sources are corrected by ground stations > via comparison > to NRL and NIST (and indirectly other sources as well). The various ground > reference > time systems get measured and evaluated to form what we call the right > time. This > is done by BIH in Paris. That process also keeps NRL and NIST “in sync” > with the correct time. > > Since everything is locked together, there really isn’t any long term > drift. As long as > everything is functioning (and the PPS is from GPS not some random > divider) you > should be “on time” to within 100 ns pretty much forever. The time > involved could > be GPS time or UTC depending on how you associate time stamps with your > PPS edges. > > If indeed something goes wrong with GPS ( as unfortunately happened to > Galileo > very recently), your time could be just about anything if the error is > undetected. If > it is detected, your will go into holdover. The drift then depends very > much on just > what “Trimble” you have inside your setup. 10 us a day for the first day > is not an > uncommon number to see. Since it’s really frequency drift rather than time > drift, > the second day will be worse and it just goes downhill from there. > > If your PPS *is* from some random divider off of (say) 10 MHz, then every > time power > goes out, it will come back up at a random point in the second. If you > punch > a button to “sync” it, you will only be able to move it in 100 ns steps ( > the period > of 10 MHz). If the 10 MHz edge is “right on” with GPS that’s fine. If it’s > off by some > random amount ….. not so fine. > > This gets into a vary basic gotcha: A typical GPSDO *does* get the output > PPS from > the 10 MHz. The PPS output direct from a GPS module probably is closer to > “on time” > that the GPS PPS. It will bounce around a lot more, but it likely is > closer to being correct. > > Lots of twists and turns …... > > Bob > > > On Jul 19, 2019, at 1:17 AM, donald collie <[email protected]> > wrote: > > > > Without wanting to show my ignorance by confusing accuracy, and > precision, > > etc, would some kind person please answer the following : Let me explain > - > > I have my prototype GPS diciplined [ Trimble inside] standard frequency > > source connected to both a divide by 5,2,5 and 2 producing all the > > reference frequencies necessary for the various bits of equipment in my > > workshop, AND the 1pps > > output connected to a 7474 "T" flipflop and thence via a 100uF capacitor > to > > a modified $10 analogue wall clock. Can anybody tell me this : If I live > > another 100 years [Let`s say I take antioxidants ;-) ] what sort of > error > > should I expect in this clock? [I know that it`s better than 1 second per > > day] > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
