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

From: Gregory W Heckler
Subject: Re: [Discuss-gnuradio] DBSRX used for GPS: cycle slip
Date: Mon, 02 Jun 2008 18:02:06 -0400
User-agent: Thunderbird (Windows/20080421)


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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