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).

Features: 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. 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