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Cellular forums Home > Archive > Magellan GPS > May 2007 > Problem with heading Explorist 600
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Problem with heading Explorist 600
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| John B. Coarsey, PE 2007-05-03, 7:33 am |
| When I am in my vehicle with GPS flat near the seat the heading value is 30
to 40 degrees off from when I lift up th unit even with the windshield. Th
latter reading is more correct but flucuates a lot. I am not using
electronic compass and when unit is flat near seat it has 7-8 satellites in
view. Also I have tried to select direction and bearing to display but these
show up as "---". The pdf guide was no help. Does anybody have any thoughts?
Thanks
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| My first (and only) thought is multi-path. It's not the amount the paths to
the satellites are changing, but the net direction that is computed from the
receiver's raw measurements. For example, I have a very new Garmin
bluetooth receiver, and when it's sitting still in the house or in the car
(whose roof is totally RF transparent), the heading estimate for one of the
programs I use is bouncing all over creation. In both of these cases, the
number of visible satellites is at least 8, and all are WAAS corrected.
How the various receivers handle multipath has improved over the years, but
the effect still is there. The problem can be aggravated by a very
sensitive receiver (which hand held receivers tend to be) due to the effect
of code cross correlation. Again, this is something that designers have
improved on over the years, but will always be unavoidable to some degree.
On 5/3/07 5:23 AM, in article 59u2ihF2mothqU1@mid.individual.net, "John B.
Coarsey, PE @yahoo.com>" <jcoarsey<nospam> wrote:
> When I am in my vehicle with GPS flat near the seat the heading value is 30
> to 40 degrees off from when I lift up th unit even with the windshield. Th
> latter reading is more correct but flucuates a lot. I am not using
> electronic compass and when unit is flat near seat it has 7-8 satellites in
> view. Also I have tried to select direction and bearing to display but these
> show up as "---". The pdf guide was no help. Does anybody have any thoughts?
>
> Thanks
>
>
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