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

[Bob Camp]

Hi

On Jun 1, 2013, at 7:42 PM, Jim Lux <jimlux at earthlink.net> 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<magnus at rubidium.dyndns.org>  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

> 
> 
> 
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