[time-nuts] Checking the Frequency of a Rubidium Oscillator

Björn Gabrielsson bg at lysator.liu.se
Tue Nov 11 18:37:27 UTC 2008


On Tue, 2008-11-11 at 10:28 -0800, Lux, James P wrote:
> 
> A GPS receiver actually solves for the state vector of the receiver (including the local clock error) using the raw observables from the tracking loop (code phase).  The nav equations calculate (apparent) range and range rate from the known state vector of each satellite and the (estimated) state vector of the receiver.  Range rate is the doppler.
> 
> The 1.xxx Megachip/second C/A code is 1023 bits long, so the classical approach is to step the receiver through all possible phases of the code, integrating at each one to see if it can detect the signal.  If your integration time is, say, 10 milliseconds, it takes 10 seconds to step through them all. Once the signal is detected, the PN tracking loop tracks that signal.

You also need to check different doppler bins. 500Hz bins are a classic
choice.

--

   Björn




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