Your plane is moving, so differential measurements using GPS works.
Human standing still, ain't.
On 1/4/2012 9:37 AM, K8RI wrote:
> On 1/4/2012 12:03 PM, Kevin Normoyle wrote:
>> Iphone uses AKM AK8975 chip to sense the earth's magnetic field (four Hall
>> effect sensors on a chip)
>> so GPS isn't providing compass. I would think it's pretty accurate. Sure
>> software and calibration, and the possibility for error, but I would imagine
>> it's really good. I have a Garmin gps/compass that senses magnetic field for
>> it's compass similarly.
> If they have an app and GPS why on earth would they want to sense
> magnetic North?
> The nice thing about my GPS in the airplane is I don't have to convert
> to get true North. With the magnetic compass you need to know the
> magnetic variation or declination and add or subtract. IIRC When I fist
> started flying it was + 5 degrees and now it's approaching - 7 in
> Central Michigan. At one time it was zero. So for 50 years our runways
> have all kept their same numbers. However they are fast approaching a
> one digit change. This far North it can vary over 20 degrees in some
> areas. In Northern Michigan it's even more than that, but due to the
> iron deposits.
> As for hams, it would seem to me that unless using a dish for EME or
> very high gain array, "That looks about right" or "North is that way" is
> close enough for tribanders and even pretty big monobanders. Those are
> the only methods I've used for over 50 years on many antennas.
> Roger (K8RI)
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