[TowerTalk] How accurate are iPhone Compass apps?

[K8RI]

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 there's
> 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.

73

Roger (K8RI)
>
> -kevin
> ad6z
>
>
>
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