The SATERN International Digital Net makes use of the FLDIGI NBEMS software suite from W1HKJ, Dave Freese. NBEMS is an acronym for Narrow Band Emergency Message System. It consists of a suite of applications that work together to provide considerable capability to the amateur operator.
Fldigi is a computer program intended for amateur radio digital modes operation using a personal computer. Fldigi operates (as does most similar software) in conjunction with a conventional HF SSB radio transceiver, and uses the PC sound card as the main means of input from the radio, and output to the radio. These are audio-frequency signals. The software also controls the radio by means of another connection, typically a serial port.
Fldigi is multi-mode, which means that it is able to operate many popular digital modes without switching programs, so you only have one program to learn. Fldigi includes all the popular modes, such as OLIVIA, THOR, DominoEX, MFSK16, PSK31, and RTTY.
Unusually, Fldigi is available for multiple computer operating systems; FreeBSD; Linux, OS X™ and Windows™.
The main window of the FLDIGI application is shown here. However, the NBEMS suite consists of not only FLDIGI providing the digital modems, but FLMSG (the text message creation tool), and FLAMP (the message broadcast application). Additiopnal applications are available from the same source HERE which will provide rig control, Net Logging, and extensions to the NBEMS suite from 3rd parties.
Online instruction for the current versions of each NBEMS module is provided in this series of links: