JTTY

JTTY is the keyboard mode WSJT-X introduced in its 3.2 test releases: RTTY-style keyboard and contest text, sent in 1.9-second frames of 4-tone FSK about 127 Hz wide, with error correction that copies far below where RTTY gives up. There are no time slots; a station starts sending whenever it likes, and the text prints as each frame decodes.

JTTY comes from the WSJT-X 3.3.0-beta4 test release, and no WSJT-X general release has it yet: the station you work needs a WSJT-X 3.2 or 3.3 test release. Nexus’s JTTY transmitter has not yet been tried on the air; check keying, power and ALC on a dummy load before you use it.

JTTY sits in the Keyboard section beside PSK: the same data privileges, the same power cap and the same USB data mode. Opening the JTTY screen makes JTTY the section’s modem, and opening the PSK screen makes it PSK again.

The tour

The header. A JTTY badge, the band picker and the frequency readout. The band picker serves JTTY’s published dials (a table marked preliminary), eleven of them from 160 m (1.838) to 2 m (144.160), with 20 m at 14.090, the main meeting place; a channel where your license class may not send data is marked RX only. Some of these dials are shared with another mode, so expect its signals in the same passband: 17 m (18.100) is FT8’s dial, 80 m (3.575) and 30 m (10.140) are FT4’s, and 160 m (1.838) is PSK31’s and RTTY’s. Opening the JTTY screen from another mode moves the dial to JTTY’s frequency on the band you are on, if your class may send data there.

Beside them are the frequency controls WSJT-X has for JTTY:

• Rx — the audio frequency the decoder always searches. Type a value and press Enter, or click a signal on the waterfall. As in WSJT-X, it goes back to 1500 Hz each time JTTY is opened from another mode.
• Tx — where JTTY transmits: its lowest tone, the other three above it. As in WSJT-X, it goes back to 1500 Hz each time JTTY is opened from another mode. The license check judges the whole signal at this offset. It cannot move while anything is queued or on the air.
• Rx→Tx and Tx→Rx — WSJT-X’s two copy buttons: Tx to where Rx is, or Rx to where Tx is.
• F Tol — how far either side of Rx the decoder always searches, from WSJT-X’s list (2 to 500 Hz). It is kept between sessions, as in WSJT-X; a new install starts at 20 Hz.

The decoder also searches the fixed 1200–1500 Hz and 1500–1800 Hz channels, but only where they fall inside the waterfall’s visible range, as WSJT-X searches them inside its wide graph. Zooming the waterfall in narrows that range.

The waterfall. A green RX cursor marks Rx and a red TX cursor marks Tx; a click on a signal moves Rx there, Shift+click (or a right-click) moves Tx, and Ctrl+click moves both. A double-click on a row decodes that stretch again (see Decode below).

The TX strip under the waterfall carries TX On / TX Off, Tune, ATU and Stop TX, as on every cockpit. Stop TX, and Esc, stop whatever is on the air. Opening the JTTY screen turns TX on, as opening PSK does, but not after a Stop: then TX stays off until you turn it on.

All decodes prints every JTTY message, in the order the messages started, in WSJT-X’s own layout: the audio frequency, the SNR and the text, wrapped at 40 characters. A message still arriving is dimmed until it ends. The head carries:

• Arm RX / RX armed — the decoder. It arms itself when you open the screen; switch Start receiving when JTTY opens off in Settings ▸ Digital ▸ PSK to arm it by hand. Stopping it yourself is remembered for the session.
• Lower case and Include time — WSJT-X’s two display options: messages in lower case, and the UTC time each message started in front of it. Both are kept.
• Erase — empties both panes. Stations already heard stay heard.
• Decode — decodes again, as WSJT-X’s Decode button does: the receive audio of the last three minutes goes through a decoder of its own, and what it finds shows in both panes under a JTTY review heading, after what was decoded live. A double-click on a waterfall row decodes 40 seconds from 5 seconds before that row. What a review finds is shown and nothing more: it is not written to ALL.TXT, spotted, or counted toward the two-decode rule below.

QSO frequency shows the messages first heard within F Tol of Rx: the station you are listening to.

On a wide window the two panes stand side by side, as WSJT-X draws them, with the log strip in a column of its own beside them. On a laptop screen they share the left column and the log strip keeps the right. ⊞ Panels in the header hides either pane or the waterfall, and shows the radio’s own scope.

If the receive audio drops out long enough for the decoder to lose its place, a line under the TX strip says so and decoding starts again.

Transmitting

The dock at the bottom of the screen is WSJT-X’s JTTY transmitter.

• The compose bar and Send — type a message and press Enter or Send. It goes out as WSJT-X sends it: a line longer than 80 characters goes in pieces, and a line break ends a message. While a message is still going, Send shows how many pieces are left; another Send queues behind it and goes on the same transmission. %M is your call, %H the call in the Call box, %E your exchange, %N the serial, %G your grid and %R the SNR of the newest decode naming the call you clicked, in the pane you clicked it in (-10 when you typed the call). A report goes only with the call it was taken for: change the Call box and it goes.
• F1 to F8 — WSJT-X’s two sets of messages, picked with Messages: Contest (CQ %M CQ, %H %E, %H TU CQ %M CQ, %M, %H, TU NOW %Q %E, %H AGN? and %E) and FT8 style for a chat-style contact (%H %M %G, %H %M %R, %H %M R%R, %H %M RRR, %H %M 73 and CQ %M %G, F7 and F8 empty). Click one or press its key. Edit keys turns the eight keys into their messages to edit, as WSJT-X’s message boxes; each set keeps its own, and Defaults puts the set back to WSJT-X’s. While you edit, F1 to F8 send nothing and say so; they send again once you finish. A message in one of WSJT-X’s contest forms (the defaults, %H %G, 599 %G, %H 599 %N, TU NOW %Q 599 %N, 599 %N, %G, and a request such as AGN?, NR? or QSL TU) goes in JTTY’s compact form; a call in it must be a standard callsign, and a key whose call is not one is refused, never sent as text. Any other message goes as text, as typed text does.
• The Call box — the other station. Clicking a confirmed call in a pane fills it.
• The serial number — what %E and %N send outside a contest, 001 and up. It moves on by one when a message starting TU goes out, as in WSJT-X, and is kept between sessions.
• Live — keeps the transmitter up while you type: your words go out as you finish them, and JTTY’s filler holds the carrier between them. Sign off sends DE <your call> K and ends it. A live session ends at ten minutes whatever you are typing.
• Ctrl+H in the compose bar types %H %M (the other station’s call and yours) where the caret is, as WSJT-X’s chat opener; Ctrl+Shift+K empties the box and stops whatever of JTTY is still going, as in WSJT-X.
• Frames — beside Send while a transmission runs: its frames on the air, of all it has queued, as WSJT-X counts them (the filler is not counted).
• Esc/Stop — cuts JTTY at once: what is on the air and everything queued.

Every send needs TX On and your license class across the whole signal at the Tx offset; a send that cannot go says why under the dock. The TX watchdog stops JTTY when nothing has been typed or sent for its whole limit (WSJT-X runs none for JTTY), and a queue too long for the watchdog is refused before it keys. Stop TX, Esc, TX Off, the watchdog and leaving the JTTY screen each stop JTTY and drop what is queued, and the line under the dock says why. Your own transmission never counts as hearing a station.

Contests

In ARRL Field Day, %E is your class and section, and F2, F6 and F8 send them in JTTY’s compact exchange form, as WSJT-X does in its Field Day mode. Winter Field Day allows JTTY for 2027. Its classes (H, I, O and M) do not fit that form, so type the exchange out (W1AW 1O WI): it goes as text, and a WSJT-X station reads it the same way. In any other contest, %E is the serial number.

Calls you can click

A call becomes clickable once it has been decoded in two separate messages within two minutes. JTTY’s frames carry a short checksum, so now and then a frame of noise decodes as text, and some of those look like real calls. A real station repeats its call; a false decode does not. So a call heard only once is plain text, and nothing looks it up.

Clicking a confirmed call puts it in the log strip’s call box, and the log strip looks it up in your callbook. The same rule keeps single decodes off PSK Reporter and off the Needed board: a JTTY station appears there, labelled JTTY, once it has been heard twice. A spot of a message that carries the sender’s grid (CQ W1AW FN31) includes the grid, as WSJT-X’s does.

Logging and LoTW

When a message starting TU goes out (F6’s TU NOW, or TU typed), WSJT-X opens its Log QSO window. Nexus asks instead, at the top of the log pane: “Log the contact with W1AW?”, naming the station the TU thanked: the one your messages before it went to, even when they carried no call (F4’s %M and F8’s %E in search and pounce). F6 thanks one station while it calls the next, whose call is in the Call box by then, so the question names the station before it. A CQ goes to nobody, whatever the Call box holds. Asking changes nothing: the Call box and the log strip stay as you have them. Log QSO logs through the strip’s own Log, with every check it makes, and only when the strip holds that call. With the strip empty, the press puts the call in it for you to check, and the next press logs it; with another call in it, nothing is logged and Nexus says so. Not now closes the question. The first answer, from this screen or a Remote one, closes it everywhere, so a contact cannot be logged twice from two screens. Logging that contact any other way (the strip’s own Log, the logbook, a Remote screen) closes the question too. If the strip cannot log it after all, the question comes back. A TU to another station before you answer replaces the question and names the one it replaced, for you to log from the strip; a question nobody answered is dropped after two minutes. When Log QSO finds the question already closed, Nexus says why: answered elsewhere, already in the log, replaced or too old. Nothing is logged unless you press it.

The log strip logs a JTTY contact as JTTY, and an ADIF export writes it as MODE=MFSK SUBMODE=JTTY, as ADIF 3.1.8 registers it. A log that holds a bare MODE=JTTY still reads as JTTY. LoTW does not list the JTTY mode yet and TQSL would drop such a contact from an upload, so a LoTW upload holds JTTY contacts back, leaves them marked as not uploaded, and says so on screen and in the connection log.

WSJT-X UDP

While the JTTY screen’s section is in use, the WSJT-X UDP Status names the mode JTTY, as WSJT-X does, and no Decode messages are sent: WSJT-X sends none for JTTY either, so a program listening to Nexus sees the same as it would from WSJT-X.