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Nexus manual · Operating

Operate — FT8/FT4 digital

The Operate cockpit is the production core of Nexus: FT8 and FT4 operating brought to operational parity with stock WSJT-X, verified line-by-line against a 207-row behavior matrix and run on the air daily. If you already operate WSJT-X, everything here works the way you expect — the sequencer state table, the decode cadence, the split arithmetic, the UDP wire format. Nexus modernizes the shell around that behavior, never the protocol behavior other operators and tools depend on.

This is the cockpit you land in when the mode switch (top of the left rail) is set to FT8/FT4. Flip it to Tempo for the TempoFast/TempoDeep chat cockpit, covered at the end of this page.

The Operate cockpit in Classic layout, receiving on 20 m FT8: the 14.0740 MHz rig readout and the mode row run across the top, a full-width waterfall sits beneath them, and the QSO strip — Call CQ, S&P, TX On, Tune, Stop TX, Hold Tx — runs under that, reading "TX — listening". Three columns fill the bottom: Band Activity scrolling at the left, the RX Frequency decodes above the Tx1–Tx6 message panel with DX Call and DX Grid in the centre, and a Stations list of callers with Work and QRZ buttons at the right.

The tour

Waterfall + decode feed. The waterfall spans the full width of the cockpit by default, between the rig controls and the QSO strip. Drag the dividers between panes to resize it (double-click a divider to reset), or use the ⊞ menu to show and hide panes; Reset pane sizes in Settings ▸ Appearance ▸ Workspace restores the defaults. Decoding is always on — there is no Monitor toggle to forget; the decoder runs every RX slot regardless of TX state. Click the waterfall to set your TX/RX audio frequency.

Band Activity scrolls chronologically, bottom-pinned, with a reviewing pause when you scroll up and period separators between T/R cycles. Every row carries annotations stock WSJT-X never had:

  • the country / DXCC entity name,
  • a B4 chip when you’ve worked the call before,
  • new-DXCC and new-grid tags,
  • CQ and YOU badges,
  • AP / low-confidence markers,
  • JTAlert highlight colors (honored over UDP if JTAlert is feeding them),
  • a teal L mark on calls known to upload to LoTW (populate the users list in Settings ▸ Logging & Connectors).

The QSO strip sits directly under the waterfall, above the decode panes, carrying your transmit controls — TX On/Off, Tune, Stop TX, Hold Tx — beside Call CQ and S&P. (These live in the QSO strip in this view; Phone and CW keep the cluster in the top bar.)

Classic ↔ Roster. A single toggle switches the layout:

  • Classic is the stock-style Band Activity view, with the Tx1–Tx6 message panel, editable DX Call / DX Grid fields, and Generate Std Msgs.
  • Roster is a modern sortable call roster — one row per station, sorted by what matters to you.

Use Classic when you want the familiar WSJT-X message-by-message control; use Roster when you’re scanning a busy band for the one call worth working.

The same cockpit with the toggle flipped from Classic to Roster. The Tx1–Tx6 message panel is gone, replaced by a wide sortable Call Roster — one row per station with CALL, NEED, COUNTRY, GRID, DIST, BRG, SNR and AGE columns, sorted by NEED so the GRID and POTA rows sit above the CNF ones, with "Needed only" and "Hide worked" both ticked. Band Activity and the RX Frequency decodes move into a narrow column on the right.

Core workflows

Answer a CQ (search & pounce)

  1. Find the station in Band Activity or the roster. New-DXCC/new-grid rows are tagged; a B4 chip means you’ve worked them before.
  2. Double-click the decode. Nexus jumps to exactly the Tx step stock WSJT-X would choose given what that station last sent, and — with “Double-click arms TX” on (the default) — enables TX so your reply goes straight out.
  3. The sequencer runs the exchange automatically: your report → their roger-report → RR73 → 73. It locks onto the worked station, so a report from a bystander never advances your QSO, and portable suffixes are matched by base call.
  4. On the final 73, TX disarms (WSJT-X default — see “Disable TX after sending 73” in Settings ▸ Modes ▸ Digital). The QSO logs automatically if Auto-log is on.

Run CQ (call and work the pileup)

  1. Set your band and audio frequency, then click Call CQ. Directed CQ (CQ DX, CQ NA, CQ POTA, CQ 040…) persists across the run exactly like stock Tx6.
  2. When a station answers, the sequencer works them, then auto-returns to CQ for the next caller.
  3. Optional guards in Settings ▸ Modes ▸ Digital: “Stop CQ after N calls” ends an unanswered run; “Auto-CQ: drop a silent caller after N overs” abandons a station that answered then went quiet.

Remember to pick your transmit period (Tx 1st / even, or Tx 2nd / odd) — the two stations in a QSO must be on opposite periods. The choice is on the top bar and in Settings ▸ Modes ▸ Digital.

Work a needed station

The Needed board ranks everything on the air by what it’s worth to your log. One click on a row QSYs band + mode + exact frequency atomically and opens this cockpit with the DX ready to work — the same atomic path as double-clicking a spot on the Connect map.

Hound a DXpedition (Fox/Hound)

  1. Turn on DXpedition mode ▸ Hound in Settings ▸ Modes ▸ Digital (or start it from a DXpedition board row).
  2. Nexus spreads your initial calls above 1000 Hz (session-salted so callers don’t stack) and auto-moves your TX to the Fox’s frequency the moment you’re answered.
  3. Multi-payload Fox frames are split and attributed safely — a bystander’s “73” can never fabricate a confirmation in your log.

Nexus implements the Hound side. The Fox role (running the DXpedition end) is not implemented.

Split, decode depth, and re-decode

  • Split Operation offers the stock trio in Settings ▸ Radio ▸ Rig Control: None, Rig (VFO B), and Fake It (TX audio held to 1500–2000 Hz with the dial shifted in 500 Hz steps for a cleaner signal).
  • Decode depth (Fast / Normal / Deep) and the decoder passband (default 200–2900 Hz) are in Settings ▸ Modes ▸ Digital.
  • F6 re-decodes the retained last period and adds only what the first pass missed. Esc halts TX, F4 clears the DX call, Alt+1–Alt+6 fire the Tx slots.

Working with the rest of the shack

Nexus speaks WSJT-X’s UDP protocol byte-for-byte, so GridTracker, JTAlert, and your logger see Nexus as WSJT-X. Outbound Heartbeat / Status / Decode / QsoLogged and inbound HaltTx / Clear / Replay / Location / HighlightCallsign all use the canonical type numbers, and PSK Reporter spotting batches on the stock schedule.

If another app owns the rig, Companion mode rides an upstream WSJT-X/JTDX decode stream over UDP (default :2237) instead of decoding itself — point it at the source in Settings ▸ Logging & Connectors.

Honest limits

  • Fox role is not implemented — you can hound a DXpedition, not run one.
  • No contest modes in the digital cockpit beyond Field Day (no NA VHF, RTTY RU, WW Digi).
  • Fox role aside, the mode list is complete: FT8, FT4, FST4, FST4W, Q65, MSK144, JT65 and WSPR all decode and transmit, alongside Nexus’s own TempoFast/TempoDeep.

The Tempo chat layer (TempoFast/TempoDeep)

Flip the mode switch to Tempo and the operating cockpit becomes a chat-first, per-station conversation surface. This is the original Tempo product, and still the novel part of Nexus: two experimental weak-signal protocols that carry the same WSJT-X 77-bit message set as FT8, so structured exchanges stay bit-compatible with the FT8 ecosystem.

Two tiers share the cockpit, selected on the dial:

  • TempoFast — a 4-second-cycle coherent waveform (~−15 dB AWGN threshold in simulation). The short cycle is the point: keyboard chat that feels like a conversation instead of a slideshow.
  • TempoDeep — a 15-second non-coherent 8-FSK robust tier, built to shrug off fading (~3.7 dB fading penalty in simulation where coherent modes lose 10+).

Nexus remembers your tier per area, so setting the dial to one tier and stepping away to another section brings you back to the same tier.

On top of the waveform:

  • Threaded per-station chat with word-wrapped chunked free text.
  • Presence / heartbeat roster — who’s on frequency and reachable.
  • Presence-gated store-and-forward — a directed message queues until the recipient is actually heard, then delivers with correct attribution.
  • IR-HARQ (on by default) — a weak frame that fails isn’t wasted; its retransmissions are joint-combined (RV0 → RV1 → RV2) until the message lands, for a simulated ~+2.5 dB / ~2× completion gain in the marginal zone. A session rescue counter in the UI shows how often it saved a frame. Toggle it in Settings ▸ Modes ▸ Digital.
  • Coordinated QSY (Roam) — an announced, plain-text, in-the-clear frequency move for keeping an off-grid net together, with deterministic timing and automatic return-home on lost sync. It is a net convenience, not privacy and not encryption; it is off by default.

Honest status of TempoFast/TempoDeep

Two questions live here and they have different answers. Do the tiers work on the air? Yes — the first over-the-air TempoFast decode was on 2026-07-21 and the first two-station Tempo QSO (KD9TAW and N9UM, 6 m) completed on 2026-07-26, which retires the question every new waveform faces. Did the threshold numbers come from the air? No. Every TempoFast and TempoDeep performance figure above is a bench number from AWGN and fading sweeps, and it is labelled that way for that reason. TempoFast does not beat FT8 on raw sensitivity — it trades roughly 6 dB of raw single-shot sensitivity for a nearly 4× faster cycle plus HARQ. What is still owed is decode rate against signal level on real paths, and an on-air report is the single most useful thing you can send. The FT8/FT4 tier carries the daily-driver load meanwhile.

This page is synced from docs/guide/operate-digital.md in the Nexus repo. Corrections belong there.