Fldigi is a computer program intended for Amateur Radio Digital Modes operation using a PC (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 DominoEX, MFSK16, PSK31, and RTTY.
Have trouble with installing and operating Fldigi? The CAT interface wont work? Follow the link below to an help page that will teach you how to install the software on some popular modem HDF radios.
Fldigi Help Page: https://sourceforge.net/p/fldigi/wiki/how_to/