[time-nuts] Home made GPS disciplined atomic clock

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Jan 27 15:16:35 EST 2009

Mark Sims wrote:
> Hello Bruce,
> The Thunderbolt documents four filters that you can enable (PV, ALTITUDE,  STATIC,  and KALMAN).  The KALMAN setting is not documented for the regular Thunderbolt.  The Thunderbolt-E lists it as being available.  Lady Heather gray's out the option unless you have a -E (but does let you try and set it if you have a normal Thunderbolt,  no telling if it actually does anything).  I think these filters are for receiver dynamics and not oscillator disciplining.
> Mark

A Kalman filter is built in to the Thunderbolt, you just cant directly
turn it on or off or set its parameters.
A Kalman filter is used to measure and store the frequency drift and
temperature drift characteristics of the OCXO and use them to improve
the holdover performance.
The altitude filter allows   the GPS receiver to ignore GPS SVs whose
altitude is too low.
The static mode is for fixed position operation where either a manually
entered or an auto surveyed fixed position is used by the GPS receiver.
This allows timing information to be derived from a single visible GPS SV.
When more SVs are usable more accurate timing information can be derived.


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