[time-nuts] Slightly OT - GPS-Based Accurate Direction Finding

Magnus Danielson magnus at rubidium.dyndns.org
Thu Aug 26 21:29:41 UTC 2010

On 08/26/2010 05:24 PM, Attila Kinali wrote:
> On Thu, 26 Aug 2010 06:58:01 -0700
> jimlux<jimlux at earthlink.net>  wrote:
>> 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.
> Yes, but for this you have either to build a GPS module yourself,
> which is not trivial (neither is it to get GPS chips in single
> quantities) or you have to get one of those GPS experimentation
> boards which are not really cheap.

GNSS samplers is off the shelf stuff for reasonable money.

> Not to mention that you are then running your own GPS code
> which is probably more than the OP was asking for.

Part of the fun. Not too hard really... got pretty far on my code already.

> IMHO it's simpler to use available precision modules that provide
> phase data and use that for the caluculation. If additional accuracy
> is required, both modules can be modified to run from the same OCXO
> instead of the TXCO they usually use.

Just using the same TCXO is a step forward. Off the shelf boards have 
been hacked for this very purpose before.

Systems for heading, tilt etc. is commercially available for both 
airplanes and boats under various names. The main system usually have 
one main antenna for positioning and additional antennas for orientation.

The critical aspect is carrier phase detection, if one has carrier phase 
reports, the rest can be done in post-processing.


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