[time-nuts] Raw GPS signal samples

[Said Jackson]

Tom, John,

Wouldn't the software be able to remove any LO instability by simple cross correlation error cancellation by all the carrier phases? After all carrier phase measurements are concerned with relative phase delays, not absolute offsets?

In other words the LO and ADC phase errors should show up on all carriers identically and at the same capture time. Assuming that the stability of the carrier phase is not degraded much by the transmission path I would think the LO errors could be reduced to levels approaching the transmission LO and Carrier stability even if just using a cheapo crystal for sampling?

From what I read using external LO feed into GPS receivers from eg an atomic clock helps re-aquisition time but not locked accuracy or timing stability necessarily?

Certainly most GPS lose lock momentarily if you breathe on them so I could be wrong, but they don't have the benefit of post processing out the LO errors..

Bye,
Said

Sent From iPhone

On Sep 4, 2013, at 14:05, "Tom Van Baak" <tvb at LeapSecond.com> wrote:

> Hi John,
> 
> It's not off-topic at all. Thanks for posting. Someday it would be cool if an amateur precise time project emerged from this effort.
> 
> What is not clear from your link is the accuracy or stability of the LO that was used. It seems to me, for timing purposes, that one would want to have a very precise timebase for the binary samples that are collected.
> 
> I suppose it depends if someone just wants to make a homebrew (50 baud) GPS subcode decoder and navigation receiver, or if someone is interested in extracting as much precise time from the code and carrier phase as possible. For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest.
> 
> Do keep us posted.
> 
> /tvb
> 
> ----- Original Message ----- 
> From: "John Seamons" <jks at jks.com>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Sent: Tuesday, September 03, 2013 1:30 PM
> Subject: [time-nuts] Raw GPS signal samples
> 
> 
>> Somewhat off-topic but it might help someone out: I've had a tough time finding, and using, files on the net containing raw GPS signal samples to be used with the various software-only (or software-mostly) GPS receivers out there. I finally got a file of data that works and have have posted it plus a description of the file format here: <http://www.jks.com/gps/gps.html> I've used it successfully with Andrew Holme's excellent homemade GPS receiver. Now on to building an actual RF front-end to get some real signals..
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.