Hi On Jun 1, 2013, at 7:38 PM, Jim Lux <[email protected]> wrote:
> On 6/1/13 12:02 PM, Scott McGrath wrote: >> True >> >> However with LORAN and to a lesser extent WWVB traceability process >> was well/known and documented and had been in place for decades and >> was easy to implement correctly With GPS not so much especially >> with S/A. Supposedly the new satellites don't have S/A but since the >> GPS satellites are primarily military in nature how will precise >> positioning be denied in emergency situations. Shut down L1?, >> dither the signal ???? Or is S/A still there and how does a T/F user >> respond to GPS not running normally??? > > SA was turned off in May 2000, and the US government has said they'll never > turn it on again (there's too many civil applications of GPS, for one thing). > The Block III satellites don't even have SA capability. > > There's also GLONASS and Galileo and various other similar systems available. > > I think the military doesn't think that "denying GPS" is a useful strategy > anymore, at least on large scale basis. Localized jammers, sure: there's a > huge amount of work on making jammers and antijam and anti-anti-jam schemes. > For what it's worth a lot of those rely on clever antenna approaches > (adaptive nulling of the jammer, for instance). > > Actually the "nail in the coffin" of SA was quite a while before it was turned off. Various people demonstrated that they could get around SA (dilution of navigation precision) while SA was still turned on. Bob > As far as how you use GPS to get time transfer in a traceable way, instead of > LORAN.. it's exactly the same, there's tons of papers out there, etc. > > I'm not sure, but I'll bet you could use the geodetic processing services > from GIPSY/OASIS or ITRF to do some sort of time transfer (after all, if you > can locate yourself to centimeters, that implies time knowledge to less than > a nanosecond) > > > >> >> Since the demise of LORAN and WWVB (although d-PSKer may allow us to >> bring spectracoms and 117a's back. >> >> To achieve traceability we have been shipping our CS and some Rb >> standards under power to labs who have achieved traceability >> >> This is is a pain to say the least. The procedures currently are not >> well documented on achieving traceability in the age of GPS only. > > I find that hard to believe. > >> >> And it's also true that most people confuse traceability with >> adjustment. In reality it's more of a chain of data with documented >> values all the way back to NIST or other national standards lab > > So many people are using GPS for time transfer, I would assume it's pretty > straightforward.. you send a check to NIST and they provide the procedure and > the paperwork. > > (the procedure is free.. but the paperwork might cost something) > _______________________________________________ > 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.
