[time-nuts] GPS backup for the stationary time and frequencyuser
Mark J. Blair
nf6x at nf6x.net
Fri Oct 8 17:38:50 UTC 2010
On Oct 8, 2010, at 10:27 AM, J. Forster wrote:
> GPS needs several birds to lock up,
To get a position fix, this is true; 3 birds minimum for a 2D fix, 4 birds minimum for a 3D fix.
> and if you look at a single bird, Dopplar will make the signal useless as
> a frequency reference.
Only if you don't already know your position. Once your position has been determined accurately and you have the current ephemeris data for the bird you're listening to, you can factor out the predictable doppler and use a single bird for timing and frequency.
Mark J. Blair, NF6X <nf6x at nf6x.net>
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.
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