GPS antenna mounting on fiberglass cars?

[Bruce]

I tested about 8 different antenna locations on my Elise yesterday. On the roof was the best and is what I used for a base line. I found on the little shelf above the interior light at the base of the rear window inside the interior to be the second best location to on top of the roof. It surprised me but that's what I found. It was a little better than in the front windshield like Michael has his. Also, I found that satellite position over the course of time has about as much effect as the antenna location. Over the course of testing (about 5 hours) results changed for the same antenna location when I tried to duplicate the results. BTW, about all the locations I tested (all but on top of the roof were under fiberglass, plastic, or glass) were acceptable.

[Michael]

Due to variations in satellite positions obviously antenna location can only be optimised by using several DL1s and antennas at the same time.

My pocket PC based navigation system with bluetooth GPS "mouse" receives more satellites than the DL1. Some SIRF3 receivers promise to work even in buildings. Can we use the progress made?

Maybe it will be possible to get better GPS accuracy with a better GPS antenna and receiver. Today's systems have SIRF3, EGNOS and WAAS integrated, not sure about this with the DL1.

Any experts can clarify this? Support?

[Bruce]

Re. the positional accuracy regarding the antenna position we found that this depends more of the circumstances on the day than the fixing. I could only find some files of the Nuerburgring, unfortunately not from the same day. My car has the antenna fitted in the foremost position under the windscreen (black line in graphs) while the other antenna sits on the brake vacuum reservoir (red line in graphs).

Michael,

What is actually being measured on the Pos Accuracy? Is it the Dilution of Precision? If so, are the commas in those numerals on the graphs acting as decimal points? Is the y-axis 2 to 5?