Nearly every digital mode runs in software. The program turns your typing into audio tones (and back), a sound card moves that audio to and from the radio, and the radio transmits it like a voice signal. The same station setup carries many modes: you change the software, not the radio.
The chain
Most modes share this chain. Only the modem and the program change from mode to mode.
The modem (the software that makes and decodes tones) is separate from the radio. The link between them has two jobs: carry audio each way, and turn the transmitter on and off. CAT control can also set the frequency and mode for you; see CAT control and rig software. Many modern radios have a built-in USB audio device; otherwise an external interface does the same job and often provides electrical isolation. See Computer and sound-card interfaces.
Categories of software
Category
What it does
Well-known examples
Weak-signal suites
Timed modes such as FT8, FT4 and WSPR
WSJT-X
Multi-mode keyboard programs
Many keyboard modes in one program
fldigi
Keyboard messaging
Free-text, weak-signal chat
JS8Call
Radio email clients
Compose and send Winlink mail
Winlink Express
Software TNCs
Packet and APRS modems
Direwolf
Rig control and logging
Frequency, mode, and contact logs
Hamlib-based tools, logging programs
These names are examples of each category, not recommendations. Features and platforms change; check what runs on your computer before choosing.
Getting a clean signal
Frequency across, time down, strength as brightness. Faint vertical lines beside a signal mean overmodulation.
Beside the signalClean
The waterfall shows frequency across, time downward, and brightness as strength. It is the main tuning tool: you see signals, pick a clear spot, and see whether yours is clean. Vertical lines on either side of a signal mean it is overdriven.
Set the audio level in the computer, not with the mic gain, so the radio's ALC barely moves. More audio does not mean more power, only more distortion.
Turn off speech processing and use a wide, flat filter in the radio's data setting.
Run well below the radio's maximum power: data modes keep the transmitter on for much of the time, so the radio runs hot.
For timed modes, keep the clock correct, using internet or GPS time.