[time-nuts] Best Chance GPS module

[Chris Albertson]

People are mixing precision timing with NTP level or timing.   That is way
the conflict in the quotes below.

If you care about nanoseconds then yes, location comes first.   You first
use the GPS to do the site survey to determine location from possibly HOURS
of data collection from a fixed antenna.  This gives a very good estimate
of the antenna location.  Then you place the GPS receiver in timing mode
where youTELL the GPS the location and it computes the time.   The GPS can
give much more certain timing if there is little uncertainty in location.
  This only works for antenna that are bolted down to the top of a
permanent mount.     With a surveyed location the error bars on the time
are smaller.   So for precision time, it is a two step process

But in the normal use case of a GPS that is turned on at some unknown
location, yes location and time come together.

There is a third mode used for marine navigation.  You can set some GPSes
to "sea level" and tell it the height of the antenna above  sea level and
then the GPS gives better location information because all of the
uncertainty is taken out of one dimension.

The people doing those site surveys are likely running precision
oscillators and worried about errors less than one part in 10 to the 10th
power.





On Thu, Dec 1, 2016 at 12:34 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

>
> kb8tq at n1k.org said:
> > The navigation solution  is something you must have before you can begin
> to
> > get a timing solution.
>
> That sounds like a 2 step process: where, then when.  Does it work that
> way?
> I thought you got where and when at the same time - you couldn't get where
> without also getting when.
>
> --
> These are my opinions.  I hate spam.
>
>
>
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-- 

Chris Albertson
Redondo Beach, California