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Setting up a station for digital modes involves connecting a radio to a computer so that software can generate transmitted audio and decode received audio. The good news is that the same basic setup works for almost all HF digital modes — FT8, FT4, PSK31, RTTY, JS8Call, Winlink, and more. Once your station is configured, switching between modes is usually just a matter of opening different software.
This guide covers the typical HF digital station. For VHF/UHF digital voice modes (DMR, D-STAR, System Fusion), the radio usually handles everything internally and no computer connection is needed during normal operation (though programming software may require a USB connection).
A digital mode station has three logical connections between the radio and computer:
The computer needs to hear what the radio receives (receive audio) and feed audio into the radio for transmission (transmit audio). This audio path is the core of any digital mode setup.
Modern radios with built-in USB audio — Many current HF transceivers (Icom IC-7300, Yaesu FT-991A, Yaesu FTDX10, Kenwood TS-890S, Elecraft KX3, FlexRadio, and others) include a built-in USB audio codec. When you connect the radio to the computer with a USB cable, it appears as a sound card. No external interface is needed.
External sound card interface — For radios without built-in USB audio, you need a sound card interface — a device that connects between the radio's audio jacks (or accessory port) and the computer's USB port. See the Sound Card Interface page for details on popular interfaces and how they work.
The computer needs a way to tell the radio to start and stop transmitting (push-to-talk). Several methods exist:
CAT PTT — The computer sends a "transmit" command through the CAT (Computer Aided Transceiver) control connection. This is the cleanest method and is supported by all modern radios with CAT capability.
Serial port RTS/DTR — The computer asserts a serial port signal (RTS or DTR) to key the transmitter. The sound card interface typically includes a circuit to convert this signal to the radio's PTT input.
VOX — The radio's voice-activated transmit triggers when it detects audio from the computer. This works but is the least reliable method — timing delays and false triggers can cause problems, especially with time-critical modes like FT8.
Hardware PTT via interface — Many sound card interfaces include a built-in PTT circuit triggered by the same serial port or USB connection.
For most setups, CAT PTT is recommended. It is reliable, has no timing delays, and does not require additional wiring.
CAT (Computer Aided Transceiver) control allows the computer to read and set the radio's frequency, mode, and other settings. While not strictly required for digital modes, CAT control is highly recommended because it allows software to:
CAT connections are typically made via USB (for modern radios) or a serial cable (for older radios). Each radio manufacturer uses their own protocol (Icom CI-V, Yaesu CAT, Kenwood command set), but software like WSJT-X and Fldigi support most radios through the Hamlib library.
If your radio has a built-in USB audio codec and CAT control via USB (e.g., Icom IC-7300):
That's it. One cable handles audio, PTT, and CAT control.
If your radio has a traditional audio output (speaker/headphone jack, accessory port, or data port) and no USB audio:
For radios without CAT control:
This works but requires more manual intervention. You will need to tune the radio by hand and may need to adjust settings manually when changing bands.
Correct audio levels are critical for clean digital mode operation. Incorrect levels cause distortion, splatter (interfering with other stations), and poor decode performance.
The goal is to produce a clean, undistorted signal from your radio with zero ALC activity. ALC (Automatic Level Control) in a radio is designed for voice peaks, not the constant-level signals of digital modes. When ALC activates on a digital signal, it distorts the signal.
To set transmit audio:
The radio's receive audio needs to reach the computer at an appropriate level — not too quiet (poor decoding) and not too loud (clipping/distortion). Most digital mode software includes an audio level indicator:
Adjust the radio's audio output level (or the interface's receive gain) until the software shows a healthy level. If using a radio with USB audio, the audio level may be controlled through a menu setting on the radio.
Many digital modes — especially FT8, FT4, and JS8Call — require your computer's clock to be accurate within ±1 second of UTC. If your clock is off, you won't decode signals properly and other stations won't decode you.
Windows: Use an NTP (Network Time Protocol) client. Windows' built-in time synchronisation is often not accurate enough. Free tools like Meinberg NTP, BktTimeSync, or Dimension 4 provide more accurate synchronisation.
macOS and Linux: The built-in NTP client is usually sufficient if configured to sync frequently.
Without internet: A GPS-disciplined clock or GPS receiver with a PPS (pulse per second) output can provide sub-microsecond time accuracy. This is the gold standard but only necessary if you operate without internet access.
Once your station is connected, the software you use depends on the mode:
| Mode(s) | Software |
|---|---|
| FT8, FT4 | WSJT-X (free) |
| JS8Call | JS8Call (free) |
| PSK31, RTTY, and many others | Fldigi (free) |
| RTTY (contest) | MMTTY, 2Tone, or N1MM Logger+ |
| Winlink email | Winlink Express (Windows), Pat (cross-platform) |
| VARA modem | VARA HF / VARA FM |
| APRS | Dire Wolf, pinpoint, Xastir |
| Logging | WSJT-X (built-in), Log4OM, N3FJP, HRD |
Most operators end up with several programs installed, launching whichever one they need for the current mode.