Wild Sanctuary wrote:
>
> Curious, then, why two different Garmins (etrex units) gave two
> different readings (altitude and location) from the same position.
> Has the Clinton order been rescinded? We were in the open, and were
> getting signals from 4 different satellites.
No, the order is permanent. The military still has the ability to mess
it up for selected areas of the world, but currently I don't think they
are using that at all. And in any case would not for the US.
4 satellites is bare minimum for accurate readings, particularly for
altitude. One that was slightly off in it's internal clock or location
data can create quite an error. That's what WAAS is for, transmits the
error corrections on the individual satellites.
It would also depend on the position of the 4 satellites. Wrong
combination (all in a small part of the sky), and the error will go up.
For that matter, did you have the two extrex in the exact same position
and orientation? It's more than just reading different, the satellite
signals vary with location. And, of course reflections vary. That's not
a big issue, but can sometimes throw one off.
Did you use averaging? If you are getting this sort of error
consistently with averaging, then I'd worry that one of the extrex or
both had problems. That's way more error than normal. I routinely have
certain points (like my house) I recheck with mine to make sure they are
functioning normally. Electronics can go bad, though these things are
pretty dependable. Repeatability of my house point location with
averaging over several years has been within 50 feet. And that's with
the old 12XL and includes before the Clinton order. Lately it's been
staying within a even tighter circle.
I've not used that model, so have no direct experience with it's foibles.
Walt
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