Some GPS Info

Here is a chart of some GPS passes over my house. This chart was generated using the $GPGSV info in NMEA output from a Rockwell TU7-D110 OEM module. The GPS module is mounted in a skylight that is on a sloping roof that faces Magnetic North (about 11.5 Deg E of True North). You can see that the view to the south is limited down to about 30 deg due to the slope of the roof. I have a view very close to the horizon to the North.
The grey lines in the chart indicate the Satellite path , but the GPS had no signal. The range of colors from 35 to 30 dB indicate the S/N Ratio (I'm not sure if '30' really means 30 dB S/N - thats a pretty solid signal! )
An interesting feature is that no satellites pass low and due South. This is because of the orbits are inclined 55 deg to the equator, meaning that they never go more than 55 deg South.

Note that each dot is a minute apart which will give you an idea of the duration of eachpass

Testing a G8 OEM GPS in the backyard
Civil Time Reciever

Here are some possibly useful GPS links
University of Montanna GPS pages.
NMEA Messages