Ham Digital Modes (FT8, PSK31, RTTY)

The single biggest change in amateur radio in the last decade: weak-signal digital modes turned a 5 W radio + a wire dipole into a worldwide DXing tool. FT8 alone now dominates HF activity by a huge margin — more QSOs are made on FT8 than every voice and CW mode combined. Cross-link with Ham Rig Control (Hamlib) for the CAT layer underneath, Ham Logging for capturing QSOs, and Propagation & Band Conditions for live-spot networks.

The K1JT family — weak-signal kings

• ★ WSJT-X — Joe Taylor (K1JT, Nobel Prize physicist) and team. The reference application for FT8, FT4, MSK144, JT65, JT9, WSPR, Q65, FST4, FST4W. Cross-platform (Win/Mac/Linux). Hamlib-based CAT control. GPLv3. Default for anyone running FT8.
  • https://wsjt.sourceforge.io
• JTDX — community fork of WSJT-X with better decoder for crowded bands (claimed 1–2 dB improvement on FT8); UI tweaks (waterfall, audio band selection, multi-decode display). GPL. Active in 2026.
• MSHV — LZ2HV's all-mode tool focused on EME (moonbounce) and contest multi-streaming. Free, closed source. Popular with serious VHF/EME ops.
• Q65 / FST4W — newer K1JT-family modes for very weak signals (EME, microwave, ionospheric scatter). Built into WSJT-X.

Conversational / keyboard modes

• ★ JS8Call — FT8-derived mode for keyboard-to-keyboard chat with weak-signal robustness. Forwarding, group rooms, store-and-forward. The "ham radio Internet, slow but always works" — popular with off-grid / preparedness ops. GPLv3.
  • http://js8call.com
• ★ Fldigi — the multi-mode workhorse. PSK31, PSK63, PSK125, RTTY, Olivia, Contestia, Hellschreiber, MFSK, Domino, Throb, MT63, CW, SSTV, Wefax. FAQ-rich, plugin-rich, on every shack PC. Cross-platform. GPLv3. The default for any non-WSJT digital mode.
  • http://www.w1hkj.com/
• DM780 — part of Ham Radio Deluxe; closed; paid. Multi-mode; pretty UI; less common than Fldigi in 2026.
• MultiPSK — Windows; closed; paid (~$45); huge mode list including obscure / paid-data modes.

Specialist tools

• WSPR / WSJT-X built-in — Weak Signal Propagation Reporter; transmits a 100 mW beacon and reports back via wsprnet.org. Beacon receivers worldwide log who heard your signal — the canonical "is my antenna working?" test.
• WSPRnet daemon — receive-only WSPR continuously; contributes to the global propagation database.
• PI4 — beacon mode for VHF/UHF; more robust than CW beacons.
• VarAC — newer "social" digital mode app, FT8-style, with chat / file transfer / store-and-forward; closed, free.
• FT8Call (legacy) — the predecessor to JS8Call; superseded.

Hardware interfaces

• SignaLink USB — classic isolated USB sound card / PTT box; ~$120. Plugs between rig and PC; the standard "ham digital interface" for 20 years.
• Tigertronics SignaLink USB / RIGblaster Advantage — same niche; mature.
• ★ Modern transceivers (Yaesu FT-991A, Icom IC-7300 / IC-7610, Kenwood TS-590SG, Elecraft K4) — built-in USB sound card + CAT interface; no SignaLink needed, just a USB cable. Recommended for new setups.
• ★ QRP-Labs QDX — see Homebrew & Ham-Flavored SDRs; $90 kit transceiver explicitly designed for FT8 / WSPR / digital. The cheapest path into HF FT8.
• Raspberry Pi as digital-modes shack PC — a Pi 4/5 runs WSJT-X / Fldigi / JS8Call comfortably; the Pi Classic Projects page covers this.

Companion / log-watcher software

• ★ GridTracker — see Propagation & Band Conditions — a map that tracks every FT8 station you decode, colored by grid square / continent / "needed for award." Plugs into WSJT-X via UDP. Almost everyone running WSJT-X also runs GridTracker. Closed; free.
  • https://gridtracker.org
• JTAlert — Windows-only; WSJT-X companion with audio alerts, log integration, watch-lists. Closed; free.
• PSKReporter spotter integration — WSJT-X reports your decodes to pskreporter.info; see Propagation page.

Practical guidance

• CAT + audio + PTT. The triumvirate. WSJT-X needs a working serial CAT connection (rig control), an audio device (in/out), and a PTT line (often via CAT command, or RTS/DTR on a serial port, or VOX).
• Time sync. FT8 / FT4 are time-slot-based (15s and 7.5s respectively). Your PC clock must be within ~1 second or you decode nothing. NTP-sync mandatory; chrony on Linux, Meinberg on Windows. The #1 cause of "FT8 doesn't decode anything."
• Audio levels. Too hot = ALC compression; too cold = no decode. WSJT-X's "Wide Graph" should show a noise floor near 30 dB; transmit ALC should be zero.
• Don't run 100 W into FT8. ~25 W is plenty; the mode works reliably at 5 W and below. Easier on the rig and the band.
• Stations near you crash your decoder. Strong local stations on the FT8 segment overload the decoder; reduce RX gain or use the JTDX decoder for better dynamic range.
• Auto-sequence + Hold TX Watchdog. WSJT-X's auto-sequence is great; the watchdog is essential — leaves a TX'ing radio when you walk away from the keyboard.

License / pricing notes

• WSJT-X / JTDX / JS8Call / Fldigi / WSPR / VarAC — FOSS (GPL) except VarAC (closed but free).
• MSHV — closed, free.
• Ham Radio Deluxe + DM780 — paid (~$100).
• MultiPSK — paid (~$45).
• GridTracker / JTAlert — closed, free.
• PSKReporter / WSPRnet — community-run, free for use; please feed back what you decode.

Pick this if…

• Default FT8 / FT4 / WSPR setup, 2026: WSJT-X + GridTracker.
• Crowded bands or contest-night FT8: JTDX (better decoder).
• Off-grid keyboard chat: JS8Call.
• Anything PSK / RTTY / Olivia / Hellschreiber: Fldigi.
• EME / moonbounce / multi-stream: MSHV.
• Cheapest entry into FT8: QRP-Labs QDX kit + WSJT-X + a wire dipole.
• Modern radio with no extra hardware: Icom IC-7300 + a USB cable + WSJT-X.