Hi everyone, I work for Raytheon Marine company and thought I could offer a little insight into SA getting turned off. There are two types of signals that can be received from the GPS system; C/A (course acquisition) and P code (precision). The P code is used by the military and some civilian applications for precise positioning (like Tomahawk missiles). The rest of us have access to only the C/A code. With S/A on, accuracy is stated as "better than 100 meters 95% of the time". With S/A off, that drops to around 15 meters so there is significant improvement. Any GPS receiver will realize this increase in accuracy. How will this affect differential? Both the land based differential and the new WAAS satellite differential systems will make GPS twice as accuracte even with S/A off. Typical differential accuracy is 1 to 5 meters. But this is great news for paddlers with handheld GPS's. JP Stohrer *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Thanks John, I flipped on my Garmin 12 this morning just to see what was happening and it seems to take me _very_ close to my known position on a topo, closer than it ever did. Yea! But I've I also noticed that my EPE (Estimated Position Error) figs were much lower than I've ever seen them, sometimes around 20 feet. I'm a little confused. My antenae and receiver doesn't display PDOP figs (lowest Position Dilution of Precision) and my understanding is that even with SA terminated, my EPE doesn't deal with DOP, but only satellite quantity and geometry. But, after monitoring it for several hours until I ran the batteries down, the EPE seemed to read in the really lower numbers. Just a bit of coincidence? Also, John or anyone else, if an EPE reads 20 feet, wouldn't that be from a theoretical fixed point and the real estimated error be a 40 ft. diameter? -Nick *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Here is a graphical depiction of the end of SA: http://www.cnde.iastate.edu/staff/swormley/gps/sa_trans.gif *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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