[time-nuts] Disciplining Rubidium

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Apr 24 18:00:35 EDT 2008

SAIDJACK at aol.com wrote:
> Hi Tom,
> that Superstar receiver only has +/-50ns 1PPS timing accuracy (typical).  
> That compares to an M12M claimed accuracy of +/-10ns corrected.
> I wonder why the receiver manufacturers don't do the math on the carrier  
> phase, and generate very accurate 1PPS signals. Is it because they don't have  
> OCXO's? Or do they need the data from USNO to do the math?
The PPS timing resolution is limited by the particular generation 
technique used.
The computational overhead in generating a very precise PPS may exceed 
the GPS receiver processors capability.
Whilst carrier phase measurements can be used to discipline a frequency 
standard, generating a precisely positioned PPS signal is somewhat more 
The PPS frequency can be very accurately controlled by using carrier 
phase data, however precisely controlling the delay between the PPS 
pulse and UTC is a lot more difficult.
> Is there any public domain software that can take the carrier phase data,  
> and give you a solution, at least a position fix with 1cm accuracy etc?
> As far as I know the M12+ was tested at USNO to within 2ns average over 300  
> hours, and I have never seen a better timing receiver measurement. But that  
> still is 2 Feet accuracy, a far cry from 1cm.
> thanks,
> bye,
> Said

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