Re: GPS interference and contests

hans wrote:

Why do you think that GPS has a bad coverage at the poles? The inclination and orbital altitude of Galileo is a little bit higher than for GPS, so there is potential for a small performance increases.

For some reason I thought the constellation was in low orbits and so had limited polar visibility. I was wrong there.

It turns out GPS uses a 25,000 km orbit, inclined at 55 degrees to the equator. The orbits reach 55 degrees north and south, which gives plenty of polar visibility. There will still be at least 4 satellites visible at any time. The satellites are closer to the horizon in polar regions so positional accuracy isn't affected, though I suppose shielding by surface features could be more of a problem than it is at lower latitudes.

However, height accuracy must deteriorate close to the pole because the satellites are never overhead: you get max vertical accuracy with 3 or more satellites near the horizon and one overhead.

I would expect that current GPS receivers have not implemented the Galileo ICD.
>
I'm certain you're right, especially about the units with the original Garmin 12 channel receivers (12XL, II+, III+, GPS35 etc), because apart from anything else its hard to imagine that these could cope with the different time codes used by GPS and Galileo. The time conversion algorithms must have been published long after these receivers were designed.

Thanks for prodding me into doing a quick search for the stuff I didn't know.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
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