[TowerTalk] Compass and GPS

[Jim Lux]

On 1/4/12 4:05 PM, Doug Ronald wrote:
>> I guess I'm not sure why some have additional sensors if it's possible to
> be as accurate, with no movement, from GPS.
>
>
>
> A GPS receiver with only one antenna cannot determine the direction it is
> pointed. Sure, with some movement X, Y, Z changes and a differential
> estimate is made. So for near-zero velocities, a flux-gate compass is used
> in the Garmins for true heading determination.
>

may not be flux-gate, these days.  There's a variety of MEMS and other 
sensors (magneto-resistive) available.  Fluxgates (at least the older 
ones) are pretty power hungry, because you need to saturate the core to 
make them work.