VisualGPS (Freeware) incorporates many advanced features found in professional programs. It's sole purpose is to display graphically specific NMEA 0183 sentences and show the effects of selective availability (SA).
Azimuth and Elevation Graph - View all satellites that are in view. Each satellite identifies its pseudo random number (PRN) and its azimuth and elevation. Also plot and print the physical mask angle. More Info »
Survey - The survey window displays both position and xDOP (HDOP and VDOP) parameters. The ability for user selectable HDOP/VDOP color thresholds for position averaging make a great utility. Also monitor Standard Deviation and effects of Selective Availability. That's not all - print the results graphically. (Click here for example print output) (in PDF format - 157K)
Signal Quality/SNR Window - Monitor satellite signal to noise ratios and see them graphically on the screen. The signal quality window will grow or shrink to accommodate number of satellites in view
Navigation - Monitor latitude, longitude and altitude
NMEA Command Monitor - View NMEA sentences as they are received