[time-nuts] GPS frequency uncertainty

[Bob kb8tq]

Hi

The whole clock error / orbit error thing can be corrected after the fact with data from 
various agencies. It impacts survey work at least as much as timing. Looking at it that
way, it does not really present a hard limit. 

The “what’s the frequency limit?” question depends on just what you mean by frequency. Is it the 
phase change over a second? ( = a one second counter gate time). In that case you are 
closer to the ppb range than ppt. 

Is it 50% of the time, 90% of the time or 99% of the time? Each step you take makes things look a 
bit worse. There (effectively) is no "100% of the time” answer to the question.  ADEV was 
invented to some degree because this had people very much tied up in knots “back in the day”. 

Do you average your readings in some way (like to get them on a frequency vs time plot)? That will impact what 
you “see” as the answer ( = 86,000 data points don’t fit  on a normal monitor screen … or printed page). 

Lots of qualifiers ….

Bob



> On Jul 10, 2019, at 2:44 AM, Perry Sandeen via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Yo Bubba Dudes!
> In a number of fascinating and highly educational for me were the explanation of accuracy by TVB and others.  I learned quite a lot, thank you.
> Bob mentioned about slight orbital variations in the GPS satellites.
> IIRC those slight variations meant that you could only reliably get about 1x10^12.accuracy.
> Would someone please expand on what the practical frequency calibration limit might be?
> Regards,
> Perrier
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