[time-nuts] OT - GPS and North

Mark Spencer mspencer12345 at yahoo.ca
Sat Nov 21 19:32:44 UTC 2009


Would Time Difference of Arrival techniques combined with an array of four closely spaced antennas work with Gps signals as a means of determing the orentation of the antenna array vs the gps satellites ? (I'm thinking traditional TDOA techniques may not work with gps signals.)

Mike Naruta AA8K wrote: 
> Yes, but it is rather difficult to manufacture an
> isotropic antenna.  Unless the antenna is oriented
> so as to present a normal hemisphere of same gain,
> it might be theoretically possible to model the gain
> versus direction, coupled with the knowledge of
> location of satellites and received strength, to
> determine the antenna's orientation with respect
> to the world.
> Now, there are lots of sources of error and
> potential ambiguities for this process.  As
> you say, it is more straightforward to use a
> magnetic field sensor.  With position information
> it should be easy to correct for true North.
> Mike - AA8K
> Magnus Danielson wrote:
>> 
>> Yes, but you don't know in what direction from the unidirectional antenna. The antenna has no sense of direction, but the receiver knows very well in what direction relative north each sat is. The NMEA stream even include the coarse directions.
>> 
>> If you has a steerable directional antenna, several antennas or moveable antenna, then you can convert the internal directions of the antenna into a north heading or heading towards anything else.
>> 
>> But a normal unidirectional GPS antenna and associated receiver will be able to know where it is and from it provide very high precision direction relative north, but unless you move it or make any other form of aid, it will not be able to show the heading... but when you move around in with the car, then it can show it relative to the current heading of the car... as that forms a vector for which you can relate an angle... to north or to your intended destination.
>> 
>> Cheers,
>> Magnus
>> 
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