On 9/4/13 2:05 PM, Tom Van Baak 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.
If you want to relate post processed data to a particular time when it
was collected, yes. Otherwise, the "sampling clock offset" is just one
of the things that is solved for.
So if you had a good low ADEV oscillator, then, by the time you've
calculated the frequency error in your oscillator at the time the bits
were collected, you could hope that it hasn't moved too far.
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" <j...@jks.com> To:
"Discussion of precise time and frequency measurement"
<time-nuts@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..
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