[time-nuts] Strange GPS behaviour

Jim Lux jimlux at earthlink.net
Sat Dec 29 20:34:12 UTC 2012

On 12/28/12 9:14 PM, Michael Perrett wrote:
> Bob,
> That is simply not accurate - if the solution rate is 1/second, then all
> parameters are solved in that time frame. There are 4 indpendent variables
> and minimal processing power is required to solve all four equations.
> Although I am not very familiar with commercial receivers, that is what
> happens in the Rockwell, Trimble and IEC military units. If the output is
> more than once per second it is *usually* an output of the Kalman Filter,
> not a "true" measurement.

how is the output of a Kalman filter not a "true measurement".. it's 
essentially the composite of many measurements, weighted by the 
uncertainty of those measurements, and, if properly setup, the 
uncertainty of the filter output is less than any of the component 

Or by "true measurement" do you mean a "point solution" at an instant in 
time, which I don't think you would get from any receiver that uses any 
form of tracking loop, because what is the output of that tracking loop 
but some estimate of the observable, filtered through the loop filter. 
After all, you need to measure/estimate both code phase and rate.

You could record raw signals off the air, and post process by 
correlating over a long time span to get a "unfiltered" measurement 
(although, I suppose the "integrate and dump" inherent in the 
correlation provides a sin x/x sort of frequency response)

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