The GSS4100 is a precision, stand-alone, single-channel, L1 C/A code GPS signal generator.
It can either run with the SimCHAN control software (PC GUI and USB cable connection) or can be controlled directly over an IEEE-488/GPIB interface with a remote command set.
Typically the GSS4100 is used to evaluate GPS/SBAS receivers and applications for the GSS4100 include design verification, production test, comparative evaluation, statistical data-generation through extended and repeated tests, and incoming product test.
It is now obsolete being first replaced by the GSS6100 and then more recently by the GSS6300 (which added simultaneous single channel GLONASS and Galileo capacity too).