What I tried to mean was to build your own atomic clock. Even if we think about WWVB > it has limitations but so does the gps. Actually when you think about the signal quality and minimum satellite requirements for the GPS, I think WWVB will beat GPS on average both on performance, precision and power requirements. The only problem with the rubidium osc is its life span. I don't have the exact figures in my head but I think you will lack precision will start to lack after a couple of years which originates from the change of the rubidium molecular structure. Also this system will be affected from temp changes and etc. I didn't work with a DS3231 so can't comment on that, need to check the datasheet but I think basically speaking - it uses a xtal osc or a similar structure to generate the global clock. Have you looked at CTMU application notes from Microchip ? It has a VERY high precision on the order of nanoscales and is a very cool system IMHO. Very simple and efficient. One can think endless range of applications via this technique. http://ww1.microchip.com/downloads/en/AppNotes/CTMU%2001375a.pdf Also if you can integrate CTMU with the rubidium osc (as reference clock only) I think you might extend the life span of the system. Maybe worth looking at, just my 2cents. On Sat, Apr 20, 2013 at 1:51 AM, Bob Axtell wrote: > On 4/19/2013 6:36 PM, Yigit Turgut wrote: > > Hey Bob, > > > > Try atomic clocks, they are precise and independent of gps. > > > > Actually, I have, but I plan to sell these trackers worldwide, and WWVB > has distance > limitations. It does OK in northern South America, but won't reach > further down. Europe > is covered va Swiss, German and UK time servers. Anybody know their > range of coverage? > > --BA > > > > > YT > > > > > > On Sat, Apr 20, 2013 at 1:11 AM, Bob Axtell wrote: > > > >> My need is precision time, nothing else. Before GPS, ships navigated > >> knowing the time > >> and the sun angle. I know where I am at, so with a precise clock, I ca= n > >> obtain the sun angle. > >> > >> It seems to me that there would be little reason to shut the time > >> service off, which only needsONE > >> bird. > >> > >> --Bob A > >> > >> On 4/19/2013 7:27 AM, RussellMc wrote: > >>>> This came up in a conversation related to solar tracking. Will the > >>>> military shut off > >>>> ALL of the GPS services, or just positioning, during a wartime > footing? > >>>> > >>>> How about time/date services? > >>> First casualty is to change to "selective availability" > >>> Accuracy drops substantially. > >>> This was the mode the system ran in fr many years when first > introduced. > >>> AFAIR this was done for 'Desert Storm'. > >>> > >>> I do not know if it is done, but you could shut it down regionally so > >>> that a portion of the globe was without service. How small and well > >>> defined you could do this would be "interesting". > >>> A very determined person could gain useful information from two > >>> satellites and possibly from one. > >>> > >>> Russia operates a GPS system (GLONASS*) that (memory says) uses polar > >>> elliptical orbit satellites as in that orbit shape they are in the > >>> high poleward part of their orbit for the majority of the time. > >>> Usefulness diminishes as you go southward. If they transmit around th= e > >>> whole orbit you MAY get some use from low altitude satellites in the > >>> southern hemisphere. > >>> > >>> > >>> > >>> Russia > >>> > >>> ___________________ > >>> > >>> http://en.wikipedia.org/wiki/Satellite_navigation > >>> > >>> http://en.wikipedia.org/wiki/Global_Positioning_System > >>> > >>> Says: > >>> > >>> Initially, the highest quality signal was reserved for > >>> military use, and the signal available for civilian use was > >>> intentionally degraded (Selective Availability). This changed with > >>> President Bill Clinton ordering Selective Availability to be turned > >>> off at midnight May 1, 2000, improving the precision of civilian GPS > >>> from 100 meters (330 ft) to 20 meters (66 ft). The executive order > >>> signed in 1996 to turn off Selective Availability in 2000 was propose= d > >>> by the U.S. Secretary of Defense, William Perry, because of the > >>> widespread growth of differential GPS services to improve civilian > >>> accuracy and eliminate the U.S. military advantage. Moreover, the U.S= .. > >>> military was actively developing technologies to deny GPS service to > >>> potential adversaries on a regional basis.[18] > >>> > >>> __________________ > >>> > >>> GLONASS > >>> > >>> http://en.wikipedia.org/wiki/GLONASS > >>> > >>> iPhone 4S, iPad Mini and HTC provide GPS & GLONASS > capability. > >>> > >>> GPS and phone baseband chips from ST-Ericsson, Broadcom a= nd > >>> Qualcomm support GLONASS in combination with GPS. > >> > >> -- > >> > >> The only place success comes before work is in the dictionary. > >> > >> VINCE LOMBARDI > >> > >> -- > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> > > > -- > > The only place success comes before work is in the dictionary. > > VINCE LOMBARDI > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .