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

Jim Lux jimlux at earthlink.net
Sat Jun 1 19:42:03 EDT 2013


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?





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