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).
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)
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