Re: [Discuss-gnuradio] DBSRX used for GPS: cycle slip

[Gregory W Heckler]

Chris:

So you are not tracking the signal in the traditional sense, only 
looking at the frequency and delay estimate of your FFT acquisition. How 
far spaced are your Doppler bins in the FFT acquisition? If you are 
using a 1 ms integration time, and hence a 500 Hz bin spacing, if the 
signal's true Doppler is towards the middle of a bin it is ambiguous 
which bin the peak power will reside in due to noise. I have observed 
that the USRP's clock is jittery (PLL tracking is only possible by 
opening up the bandwidth beyond the recommend 18 Hz for a 3rd order 
PLL), however I have never observed a 500 Hz instantaneous jump in 
frequency (which would cause all of the channels to dump). Do you have 
tracking data with multiple SVs which also point to a 500 Hz frequency jump?

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