Re: GPS ques

From: robert egri (rge11x_at_netscape.net)
Date: 09/11/04 

Date: 11 Sep 2004 08:24:11 -0700

mold-guardian@comcast.net (Myxococcus xanthus) wrote in message news:<ce5e7813.0409101903.4847c23d@posting.google.com>...
> rge11x@netscape.net (robert egri) wrote in message news:<b4e32a30.0409100714.1174fba6@posting.google.com>...
> > mold-guardian@comcast.net (Myxococcus xanthus) wrote in message news:<ce5e7813.0409100235.478fe5f4@posting.google.com>...
> > > Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413F3EEF.4DEBBD50@hate.spam.net>...
> [...]
> > >
> > > Show me the calculations, Al. Or admit your mistake.
> > >
> > > Making mistakes isn't the end of the world, Al. I've made several in
> > > this thread as well as in the GPS versus source dependency thread.
> > > Being able to admit mistakes is one of the factors distinguishing
> > > legitimate contributors in these newsgroups from crackpots.
> > >
> > > Myxococcus xanthus
> >
> > Instead of telling UA to admit his "mistakes", open a book and learn
> > about phase locked loops.
>
> What do PLLs have to do with the question that I presented to Uncle
> Al?
>
> Are you claiming that there is sufficient data in the problem I
> presented to compute the distance to the billboard?
>
> Are you claiming that Uncle Al is correct, that "one GPS satellite
> puts you on the surface of a sphere"?
>
> Myxococcus xanthus

A 1st order PLL will null a phase error of a signal of the same
frequency as that of the loop's VCO but with different initial phase,
a 2nd order PLL will track an initial frequency difference without
error, a 3rd order loop (usually a tricky thing to design) will track
a frequency ramp, etc. The common GPS receivers employ 2nd order loops
to track (if you wish, compensate for) the Doppler shift and
oscillator freuqncy uncertainties (temperature drift, ageing, etc).
There is no need for a rubidium clock in one's hand, a few seconds
(depending on the signal strength) and the local tracking loops will
be locked and then you have something that "ticks" as well as an
atomic clock. (OK, the local replica has more phase noise but the
average is the same).

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