Hi On Jun 1, 2013, at 7:42 PM, Jim Lux <[email protected]> wrote:
> On 6/1/13 2:51 PM, Magnus Danielson wrote: >> On 06/01/2013 11:27 PM, Bob Camp wrote: >>> Hi >>> >>> On Jun 1, 2013, at 3:34 PM, Magnus >>> Danielson<[email protected]> wrote: >>> >>>> On 06/01/2013 09:02 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??? >>>>> >>>>> A colleague of mine runs a cal lab. Guy is a wizard with physical >>>>> and electrical standards >>>>> >>>>> I run some of my gear there in exchange for calibration of my >>>>> instruments as lab has temp / pressure / humidity controls for >>>>> physical standards so we both benefit. >>>>> >>>>> 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. >>>>> >>>>> 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 >>>> >>>> NIST offers a calibration service which gives time and frequency >>>> calibration to NIST using common view GPS. Essentially that's a box >>>> being placed at the location you feed with your local signals and the >>>> box will communicate back to NIST and create the calibration records. >>>> >>>> The pieces in this, isn't all that magic and esoteric, but put >>>> together in good way and with routines to put it all together. >>>> >>>> How to do it properly when getting the NIST service is much more >>>> fuzzier. I have not seen a description of how it should be done, but >>>> it should be possible to achieve in principle. >>> >>> You do the same thing they do. You both watch the same sat(s) and >>> compare to it / them. If you are in the US, you can do common view. >>> There are LOTS of papers on how to do all that. >> >> Oh yes, but how many of them actually achieve legal traceability? >> >> Another interesting sub-set would be to ask the question if legal >> traceability can at all be achieved without active participation of the >> NMI of choice, such as NIST. >> > > > I would think not. The primary reference has to be involved somehow. > ALthough.. NIST does publish measurements they make or the level of precision > of transmitted signals. > > If I receive WWV, and measure it appropriately, can I say that my time, > accurate to 1 second, is traceable to NIST, since they broadcast it quite > accurately, and I can bound the uncertainty contribution from the propagation > and electronics to less than a second. > > That is, NIST certifies publicly that WWV is "on frequency" and "on time" > with a certain precision. Do I need to go to NIST and pay them to give ma > piece of paper that says this, or can I use their published data? Remember - the original post (and thus the context) is "legally traceable". That's (as mentioned in the original post) the land of lawyers rather than the land of engineers. Bob > > > > _______________________________________________ > 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.
