FWIW, I've worked some with a compass function on my Android phones (two
different ones).
I am not all that impressed with the accuracy. Its OK for getting things
roughly right, like within 5 or 10 degrees, but I'd want something better
for, say, calibrating a rotor.
The problem is, the phones are just too small. It is too easy to make a
"parallax" mistake.
At the least, I'd want to use a larger tablet when trying to use it for
something this important.
Also, on Android, I've tried a couple of compass programs. One appears to
use GPS, the other just the magnetometer. The GPS one appears to me to be
much more accurate. I don't know how any magnetic based phone compass
knows what the current offset from true north is. Recall that in a lot of
places, the magnetic pole lines vary -- sometimes pretty substantially --
from north. If one such is at your tower site, well, you're stuck unless
your compass software uses a GPS.
WO7R
On Wed, Dec 24, 2014 at 10:44 AM, James Wolf <jbwolf@comcast.net> wrote:
> I can't speak for all smartphones, but those that use real magnetic
> information for direction use a magnometer. Some use a 2 axis and some a 3
> axis.
> With the latest chips, there is some compensation for any close magnetic
> material during calibration, but it can't do it all. The closer you are to
> other magnetic objects the more error will be introduced. Calibration done
> correctly is also somewhat critical.
>
> The use of a demagnetizer on the phone is sometimes needed to remove
> residual magnetism to get accurate results. The wildcard is this: How
> much magnetic material is in the phone and how accurate do you need to be.
> The chips are usually accurate to about 1 degree, but that is usually
> optimistic when installed in the final device.
>
> Jim - KR9U
>
>
> ------- Original message -------
> > From: Wayne Kline <w3ea@hotmail.com>
> > To: towertalk@contesting.com
> > Sent: 23.12.'14, 21:37
> >
> > OK I do not want this to morph into the many proven ways to find
> > TRUE north.
> >
> > The compass extra on a I phone..... True north .... I assume it is via
> > GPS tribulation ??/
> >
> >
> > Wayne W3EA
> >
> > PS Merry Xmas and Hpy Holidays to ALL TT'ers
> >
> >
> > _______________________________________________
> >
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