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?
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