[time-nuts] GPS PRN vs SV...??

Björn Gabrielsson bg at lysator.liu.se
Sat Feb 9 17:26:08 EST 2008


On Sat, 2008-02-09 at 17:12 -0500, michael taylor wrote:
> On Feb 9, 2008 4:58 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
> >
> > This indicates that the receiver can see SVN 23 (PRN 32) with no difficulty.
> > However for a supposedly 8 channel receiver it sees 11 SVs??
> 
> I suspect that as long as less than 8 SV are being tracked (6 in your
> sample), it only needs one channel to "not" track the other 5 SV. The
> not tracked SV are not necessary being updated in a timely fashion so
> a one or more unused channels could be used to cycle through all SVs /
> PRNs from the almanac to look for new SV visibility and see if any of
> the not tracked SV have become suitable to track.
> 
> -Michael Taylor

Hi Michael,

You only need to track one SV to get almanac (coarse ephemeris) data for
the whole constellation. Almanac data gives you SV position within a few
km, which is plenty good for visibility calculations. However to have
current ephemeris data you would need to cycle an unused channel through
the visible SV every so hour. 

--

   Björn




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