[time-nuts] Traceability after loss of LORAN and WWVB

[Bob Camp]

Hi

On Jun 1, 2013, at 7:38 PM, Jim Lux <jimlux at earthlink.net> 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)
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