[time-nuts] OT - GPS and North

Mike Naruta AA8K aa8k at comcast.net
Sat Nov 21 19:20:25 UTC 2009


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
> 



More information about the time-nuts mailing list