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Re: LF: Coherent decoding using GPS ?

To: [email protected]
Subject: Re: LF: Coherent decoding using GPS ?
From: Alberto di Bene <[email protected]>
Date: Wed, 15 Dec 2004 22:51:07 +0100
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Wolf DL4YHF wrote:

Alberto, can you share your results with me ? I'd like to know the jitter of the 1-pps-output, and how the unit works when there is very limited view of the sky (which is the problem here, and also the reason why I haven't given up the idea of building a Loran-disciplined reference yet).
Wolf,
sure, as soon as I will have found the exact specs of this GPS, I will send them to you.
But from a "feature sheet" about it, it is possible to read :
------
• Enhanced algorithms provide superior navigation performance in “urban
canyon” and foliage environments
• Adaptive threshold-based signal detection for improved
reception of weak signals
------
The jitter specs, although I haven't found any number for them, judging from similar units, should not be spectacular, on the order of a few hundreds of ns. This means that in writing the software for your GPSDO you will have to filter it more heavily. I have experimentally found that a Kalman filter does wonders for this. The other side of the medal is that the error signal will react much more slowly to phase changes of the oscillator, which in turn implies that you will have to use a very good OCXO, e.g. an HP 10811 and not an Isotemp as I have done in my GPSDO project. So my advice is to get hold of a 10811 on eBay before
they are all sold and disappear....

73 Alberto I2PHD




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