Cons for WAAS

There are many cons. Do a search for WAAS. One thread is: http://www.poi-factory.com/node/5698

And better accuracy with WAAS isn't always true.

RT

Thanks for the link. I read it all and it answered all my questions and concerns. I couldn't tell any difference except that I thought the startup time was much longer with the WAAS enabled. It is now turned off. Thanks again.

As pretty much covered in the earlier forum discussion, WAAS is not designed to enhance accuracy below 3,000 ft above the average terrain. The other system in use by the US Department of Transportation is Differential GPS which uses high power transmitters on the ground at different frequencies than the sat GPS signals. This system is used by surveyors and can give accuracy down to a couple of centimeters. But DGPS isn't everywhere and the equipment is bulky and expensive.

As you may know, there is a 24 satellite constellation used for GPSing. These 24 satellites are constantly orbiting around the planet. WAAS, however, is geostationary. This means that it sync’ed with the earth’s orbit and therefore is always in the same place in the sky. As a result, I’d say it is unlikely to take longer to acquire since the satellite is in a known location in the sky.

.... And with this comes the problem that the satellite is lower in the sky, someplaces less than 10 degress above the horizon. This causes problems with maintaining 'lock' because of ground interference, buildings, trees, etc. This equates to longer access time.

Real time measurements taken on the same road, same time of day, traveling in the same direction, same atmospheric conditions, and at the same speed show that 'sometimes' access time IS longer with WAAS.

RT