Attila Kinali wrote:
On Thu, 26 Aug 2010 11:04:01 +1000
David Smith <[email protected]> wrote:
The system seems to work by taking the raw satellite phase information
from two separate GPS systems and crunching the data to come up with an
azimuth figure. Has anyone heard of a (Open Source?) program that could
be used to do these calculations?
AFAIK there is none out there (at least i've never seen one).
But it should be not too dificult write the software yourself.
The bigger problem is to get GPS receivers that provide you
with accurate phase information. Especially with a small baseline
you either need to sync the clocks of the two receivers or have
receivers with precise TCXO and take some additional samples to
calculate the frequency difference/drift. The precision you get
will mostly depend on the baseline and the number of samples you
use. The longer you have time to measure, the smaller your error-band
will be.
If you get a bit "closer to the metal" you could use two GPS L1 samplers
running off a common clock, and do the PN code acq and track, which
would give you carrier phase. If you do the nav solution, you know the
"look angle" to the various SVs, which would tell you the phase
differential vs azimuth.
I believe that there are open source codes out there to do the
processing. The data rate isn't all that high.. the GPS samplers are 1
bit. There's certainly lots of papers from grad students on this kind
of thing.
If you aren't concerned about acquisition time, and you can get the
ephemeris from somewhere else (so your initial guess for acquisition
isn't too far off), acquiring the signal isn't difficult.
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