[time-nuts] Positional accuracy of the M12+T

Randy Warner Randy at synergy-gps.com
Thu Jan 4 12:59:48 EST 2007


Good points. I think that a lot of people are unaware of the diurnal
shifts that occur due to atmospherics. These can be many 10's of
nanoseconds compared to UTC. This is true for every receiver I have ever
worked with. The ionospheric correction algorithms are good, but they
are not perfect. Can't wait for a civilian L2..................... 



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Thursday, January 04, 2007 9:13 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Positional accuracy of the M12+T

[ sorry, let me try that again ]

> Hmmm... with 25m position accuracy (and 100ns is about 30m), how do 
> they really get time down to a few ns. Clever engineering!  :-)

You're comparing apples and oranges: accuracy and stability.

The 25 m value you often read is probably a valid figure for the
positional accuracy of an M12.

But do not confuse this with the "few ns" timing value you read about
here. No one I know has an M12 that is accurate to a few ns. What many
of us have are
M12 that exhibit residual timing jitter of a few ns, when properly
sawtooth corrected and averaged over time compared to a local cesium

In other words, a properly filtered M12 is *stable* to a few ns over
some time frame. But it's highly unlikely it is *accurate* to a few ns.
A couple of ten ns is much more likely. And this is in the same ballpark
as the
"25 m" positional value.


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