[time-nuts] GPS backup for the stationary time and frequencyuser

Magnus Danielson magnus at rubidium.dyndns.org
Fri Oct 8 20:21:39 UTC 2010

On 10/08/2010 07:27 PM, J. Forster wrote:
> I've been half following this thread and can't make out the reason for a
> less than hemispheric antenna pattern. GPS needs several birds to lock up,
> and if you look at a single bird, Dopplar will make the signal useless as
> a frequency reference.

If you target the WAAS, EGNOS or SBAS birds you have significant less 
doppler since they sit on geostationary orbit. However, since these 
orbits is not perfect circular but slightly elliptic, so a 24 h pattern 
evolves. Just squaring up, as proposed earlier in the thread, will 
suffer from these shifts. Also, ionospheric and tropospheric delays also 
plays in, but the point of these birds is to provide improved 
predictions so a good receiver should be able to handle it. You also 
rely on the time of the base-station, but that is obvious I hope.


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