[ntp:questions] Re: PPS SYNC DISABLED

David Woolley david at djwhome.demon.co.uk
Sat Aug 12 13:48:05 UTC 2006

In article <1155356115.545749.124090 at h48g2000cwc.googlegroups.com>,
Eugen COCA <ecoca at eed.usv.ro> wrote:
> Thomas Laus wrote:

> > It should happen twice a day, nearly 12 hours apart.  Each GPS satellite
> > is in an approx. 12 hour orbit.  Your view of the constellation is the
> > same about every 12 hours.

True statement.

> hours. But, in a fixed point on the Earth, a receiver do not see one
> satellite for 12 hours ! And, the algorithm implemented in the receiver

He never said that one satellite was seen for 12 hours.  Or at least
not in the quoted bit.

> select the strongest signal from those received one time. So, the
> receiver locks on several satellites over a day.

A non-site surveyed receiver needs at least four satellite before it can
even solve for time and should use all of those in view to reduce the

A site surveyed receiver could use one satellite, but ought to use all of
those in view.  Signal strength is not a good measure of which is the
best satellite.  

(As a pedantic point, for any one satellite there will be points on the
earth that see it for a complete orbit.)

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