[time-nuts] TruePosition GPSDO Holdover Issues

[Gabs Ricalde]

On Sun, May 13, 2018 at 10:57 PM, Artek Manuals
<Manuals at artekmanuals.com> wrote:
> Nigel
> As I recall there is more to it than just the number of satellites.
> involved. Also factored in to all the math is the signal strength of the
> sats plus there relative angles to your spot on the earth. If all three are
> directly overhead the solution is not that accurate compared to if they were
> all at 45 degree elevation at widely divergent compass points gives a much
> more accurate solution . Likely the math / firmware has a quality factor
> built in depending on all the above factors not just the number of sats
>

Hi,

For a position/time solution, the dilution of precision (DOP) depends
on the number of satellites and the satellite geometry. When a timing
receiver is in 1D (position hold) mode, the TDOP is just 1/sqrt(# of
sats).