> Shouldn't a GPS unit be able to determine the present time much more
> quickly than a position fix? Sure, getting super-accurate (<<1sec)
> time will require multiple satellites, but I would think that a single
> satellite is all that is needed for a basic timestamp.

I wondered about that when I wrote that post.
That was partially what led to my 1=3D somewhere, 2 =3D torus, 3=3D 2 point=
s
comments - as Sean noted, as you get more satellites you initially get
a shrinking locus of position and then from 4 up yopu get more
accurate position BUT time data is present in every signal. Note
though that while a typical GPS unit provides a 1 Hz square wave
output, the accuracy of the edge timing of that square wave is
awesome-accurate, and the awesomeness increases with position
precision. When the system does not know where you are located it can
give you standard time but not yopur local time. If you are stationary
you can derive precise local time from std time (UTC) but it does not
'know' that you are able to do this.

It's been "some years" since I played with GPS at the output analysis
level, but I recall that the NEMA data indicates the number of
satellites in a solution and a flag that says whether the data is
considered valid or not.
You start getting decipherable position output before it has enough
satellites in use to be able to declare the result valid. Whether it
does this with its time signal is tbd - and Google probably knows.

A look through a dozen or so Gargoyle found documents which seemed
most liable to help, didn't help.
Results will depend on your receiver model. A receiver that gets UTC
with one satellite may decide not to tell you so.


   Russell
--=20
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