TIL!

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Fldigi is a free and open-source program which allows an ordinary computer's sound card to be used as a simple two-way data modem. The software is mostly used by amateur radio operators who connect the microphone and headphone connections of an amateur radio SSB or FM transceiver to the computer's headphone and microphone connections, respectively. This interconnection creates a "sound card defined radio" whose available bandwidth is limited by the sound card's sample rate and the external radio's bandwidth. Such communications are normally done on the shortwave amateur radio bands in modes such as PSK31, MFSK, RTTY, Olivia, and CW. Increasingly, the software is also being used for data on VHF and UHF frequencies using faster modes such as 8-PSK. Using this software, it is possible for amateur radio operators to communicate worldwide while using only a few watts of RF power.

https://en.wikipedia.org/wiki/Fldigi

these days every radio has a USB port, and when plugged into a computer, shows up as a full duplex sound card plus a serial port in devices. The serial port can be used simply, or you can use the CAT interface over serial, which lets you change frequencies, modes, adjust output power, and so on. Some radios have additional interfaces for "remote waterfalls" or additional IQ "audio" for SDR software to handle the decoding, where your radio becomes just a dumb pipe and does no filtering at all.

It's all real slick, but apparently WSJT-X software (made by an academic, not meant as a slur) is slicker, and nearly everyone uses that now. It isn't designed for "rag-chewing", it's designed for propagation testing and "contesting"; it's real dull after you've made dozens of contacts really far away.

Lately when i actually transmit with fldigi, i will use a web SDR like kiwi to "listen" to myself. Since the radio has a soundcard, and my PC has a soundcard, i can route websdr to one "modem" and my radio to another, and decode my own transmissions.

that's also boring!