[aprssig] How gps works

[Bob Burns W9RXR]

At 02:34 AM 5/6/2012, Stephen H. Smith wrote:

>When you get into the "urban canyons" of high-rise big city downtown 
>areas, GPS units frequently "go nuts" due to signals being blocked, 
>and by apparent time delays for given satellites abruptly changing 
>due to multipath reflections off glass-faced buildings.

I have personally experienced this on Monument Circle in downtown 
Indianapolis. Most of the buildings that face the Circle have 
_curved_ walls with large amounts of glass. Within a block or two 
from the circle are the tallest buildings in Indianapolis. A track 
recorded by a GPS receiver while driving around the Circle doesn't 
necessarily draw a perfect circle thanks to the reflections of the 
satellite signals.

Bob...