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Re: [Discuss-gnuradio] GPS with DBSRX, Almost There

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] GPS with DBSRX, Almost There
Date: Wed, 07 Mar 2007 14:34:57 -0800
User-agent: Thunderbird (X11/20070302)

I've noticed that the DLL of my software receiver settles to +15 Hz, and the true IF is +24 kHz from the predicted IF. This would indicate that the 64 MHz board clock is ~1 kHz from its spec value. This, in itself is not a problem, but I was wondering if this was within tolerances of the onboard XO?

24 kHz off at 1575 MHz would be 15ppm, which is within the spec of 50 ppm.

The real problem lies in the fact that the carrier tracking loop (a 3rd order PLL) of my software receiver cannot achieve phase lock. The phase jitter looks high, and the LO frequency drifts so much it dominates over the Doppler derived from satellite motion.

Yes, the clock does have a lot of drift relative to the doppler change rate.

If anyone would like any GPS IF data I would be happy to email it to your personal email address (indicate how many seconds of data you would like). Thanks!

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