What Nexus does

The full list, grouped the way you operate. Everything here ships in Nexus 1.21.0, and anything the app marks Beta is marked Beta here too.

Modes

Every mode Nexus decodes, it also transmits. Each of the WSJT-X modes was checked by transmitting from Nexus and decoding the result in stock WSJT-X, rather than against Nexus's own decoder, which shares its source and could share a mistake.

Mode	Notes
FT8	The core of Nexus. The QSO sequencer follows WSJT-X and is tested against a 207-row behavior matrix.
FT4	The 7.5-second mode, on the same sequencer.
FT2	Compatible with Decodium: FT4 with half the symbol time, on 3.75-second periods.
Q65	Matched sample for sample against WSJT-X's own generator, at 0.9985 correlation.
FST4 · FST4W	For LF and MF. FST4W beacons on a percentage schedule and never touches the QSO sequencer.
MSK144	Meteor scatter. It waits twelve transmit periods before giving up on a contact, where FT8 waits three.
JT65	Transmit and receive, on JT65's own frequencies.
WSPR	Beacons on a percentage schedule, on the WSPR frequencies (14.0956 MHz on 20 m).
JS8	Keyboard messaging compatible with JS8Call on the air: all four speeds decoded at once, directed messages, relay and store-and-forward. On from the first launch.
TempoFast · TempoDeep	Our own weak-signal modes, described further down.
RTTY	Sound card AFSK or a true FSK keyline, with a hands-free auto-sequencer.
PSK31 · QPSK31	Keyboard chat at 31.25 baud. A click on a trace nets the decoder without moving the rig, and you can type straight into a transmission while it is on the air.
SSTV	Any picture that arrives decodes on its own and appears where the waterfall was, then goes to a gallery with its mode, frequency and time. Sending is one press of Send.
APRS	Position reports, Mic-E, messages and status packets, on a map drawn with real APRS symbols, and a receive-only iGate.
SSB · FM	Phone with the bandscope, a six-slot voice keyer, and repeater shift and CTCSS.
CW	Keying through CAT, a serial keyline, a K1EL WinKeyer or the sound card, with an AI decoder (the DeepCW model by e04).

Each mode keeps its own rhythm and its own calling frequencies, from WSJT-X's frequency table. Rover calls (/R) keep decoding outside contest mode, where upstream 3.0.2 drops them.

−21.3dB

Nexus decode floor

−20.7dB

stock WSJT-X, same audio

The FT8 and FT4 decoder is built from WSJT-X's DSP sources (tracking 3.0.2): on the same recorded audio it decodes down to −21.3 dB against stock WSJT-X's −20.7 dB, with no false decodes, and fed pure noise it returns nothing.

The Phone cockpit on 15 m. The dial reads 21.2000 MHz with the USB, LSB and FM mode chips beside it. A bandscope fills the upper half, a panadapter trace over a scrolling waterfall. Band Activity and the six-slot voice keyer, F1 CQ through F6 Again, stack in the left column, and the log runs down the right. Push to talk sits in the dock across the bottom. — **The phone cockpit:** the bandscope, the voice keyer and the log, in one screen.

Radios and the rest of the station

Most radios connect with nothing else installed. On the radios that can stream it, Nexus shows the rig's own spectrum.

Connection	Radios	What you get
Hamlib, built in	Most CAT radios: Yaesu, Kenwood, Elecraft, Xiegu and the rest	Frequency, mode and PTT, with click-to-tune and drag-a-passband on the audio scope. Hamlib is inside every download, on every platform.
Icom over CI-V	IC-7300, IC-7610, IC-9700, IC-705, IC-905	Nexus's own CI-V connection, with the radio's spectrum scope as a real panadapter.
Icom over the network (Beta)	IC-7610, IC-9700, IC-705, IC-905, IC-7760, IC-7300MK2	On your LAN or Wi-Fi with no bridge program in between. Receive and control only.
FlexRadio	SmartSDR radios on your network	Through the SmartSDR CAT app and DAX, the way WSJT-X connects, or through Nexus's own Flex client (Beta) with the radio's panadapter, DAX audio and native meters.
Shared with other programs	wfview, and anything that speaks rigctld	Nexus shares wfview's rigctld, and its own rigctld-compatible port lets other programs share a radio through Nexus.
Two or three radios	Any mix of the above	A routing table in Settings sends each band and mode to the right radio, first match wins, so a 2 m FT8 spot and an APRS tune can go to different rigs.
Interfaces	Digirig, RIGblaster	Recognized by name when you click Detect, and paired with their sound device.
Amplifier	SPE Expert 1.3K-FA, 1.5K-FA, 2K-FA; Elecraft KPA500, KPA1500	On its own serial port: power out, SWR, supply voltage and current, temperature and the amplifier's own alarms, with Standby/Operate and band in the operating screens. Readings clear the moment the amplifier stops answering. Nexus has no command that switches an amplifier off.
Rotator	Anything rotctld drives	Point at a station from the map, or at the station in your log entry.

The Radios page lists every radio by name, with how each one connects.

Contesting and Field Day

Contest mode is one switch for whichever contest you pick. It stays off until you turn it on, because it reshapes the program for the weekend.

	How it works
Contests	ARRL Field Day and Winter Field Day (on the 2027 rules), ARRL November Sweepstakes (CW or phone), the ARRL January, June and September VHF contests, CQ World Wide DX (CW or SSB), CQ World Wide RTTY, CQ WPX (CW or SSB), and the California, Illinois, New York, Ohio, Tennessee and Texas QSO parties.
The keyboard	In the CW, RTTY and phone log strips: Enter Sends Message (off until you turn it on), the standard contest F-key layout, Ctrl+D twice to take back the last contact and Ctrl+Y to fix one in place.
Calls as you type	Super Check Partial lists the active contest calls that match what you have typed, from MASTER.SCP, and an imported call history file fills in the exchange. Unassisted mode turns both off.
The score	In every log strip while a contest runs: points, contacts, multipliers and your rate over the last ten contacts. Field Day scores against all 85 ARRL sections.
FT8 and FT4	Running calls CQ and works whoever answers; S&P answers the first CQ it hears. Each contest sends the messages WSJT-X sends in it.
A second operator	The contest logger window lets a second person log at a second monitor and keyboard. It shares the contact you are both typing and never transmits.
Club sync	Every laptop in the club runs the same contest under its rules, on the club's log with shared dupes. The club board shows each position in a band × mode grid, and a scoreboard is made for a TV across the room.
After the contest	Cabrillo 3.0 (CQ WW and CQ WPX files carry the category, club, name and email lines CQ asks for), live feeds to N1MM+ and N3FJP, and a Contest over? checklist that merges the log, exports it and puts back what the contest changed.

Chasing, awards and the map

Your log drives all of this: the Needed board, the award totals and the coloring on every decode and spot.

	What it does
Needed board	Every station on the air, ranked by what it would add to your log: a new country first, then a new zone, band and so on. Each row carries its evidence, such as heard by K9LC (EN52, 26 km) + N9CO (62 km), 4 min ago, and one click puts the radio on that band and mode.
Alerts	Cluster and skimmer spots are scored against your log as they arrive. A needed station plays a tone, even when Nexus is not the window you are looking at, and shows a banner that offers a one-click Work. A desktop notification is there too.
US states	A callsign-to-state index built from the FCC license file, so a new state shows on CW, phone and cluster spots that carry no grid.
Awards	DXCC, Challenge, Honor Roll, WAS, WAZ, VUCC per band and IOTA, worked out from your own log on your own computer. An eQSL or QRZ match shows as confirmed but does not count toward DXCC or WAS, because those awards do not accept it.
DXpeditions	A calendar with one bar per operation and its announced bands, the modelled best band and time to work each one from your station, and alarms.
Propagation	A 3-D globe with the greyline, live spots and propagation layers; predictions from a built-in ITU-R P.533 engine; and an openings detector that weighs reports from receivers near you.
POTA and SOTA	Live activator spots and one-click hunting, with the reference tagged on your contact for upload.
Satellites	Pass schedules, a polar plot of each pass, Doppler correction and rotor tracking.
Memories and repeaters	Curated memory packs, recall with Ctrl+1 to Ctrl+9, reminders for your nets, a repeater search and a CHIRP CSV round trip.

The DXpedition calendar. A What to chase list at the top names RI1FJZ in Franz Josef Land starting tomorrow, KH0N in the Mariana Islands and KH8WW in American Samoa starting in two days, and S79 in the Seychelles in three. Below it a month grid, Monday to Thursday visible, carries one coloured bar per operation across the days it is on the air, today outlined. — **The DXpedition calendar:** what to chase this week, and one bar per operation across the days it is on the air.

Logging and confirmations

	Detail
Uploads	Each contact goes to LoTW (through TQSL), QRZ, ClubLog, eQSL, HRDLog, Cloudlog or Wavelog, DXKeeper and your contest logger, as you set them up.
Corrections	Fixing a busted call sends the corrected contact to the logging services again.
Confirmations	LoTW brings in your whole confirmation history, and each confirmation lands on the contact it confirms. Every confirmation keeps its source.
ADIF	Import from any logger, with duplicates skipped, and export at any time.
Backups	A plain ADIF copy of the log kept up to date beside the database, and dated backups taken by themselves, including one before any change that would make the log smaller.

Other programs Nexus works with

You can run Nexus beside the programs you already use, and it feeds your logger and your alert program the whole time.

Program	What happens
WSJT-X UDP	Nexus sends the WSJT-X UDP messages, so JTAlert, GridTracker and your logger see a WSJT-X.
Companion mode	Work from the decodes of a WSJT-X, JTDX or MSHV that keeps the radio.
CAT sharing	A rigctld-compatible port, so other programs share the radio through Nexus.
N1MM+ · N3FJP	Each contact is sent as you log it, in a contest or not.
DXKeeper · Cloudlog · Wavelog	Each contact goes to DXLab's logger or to your own Cloudlog or Wavelog server.
LoTW · QRZ · ClubLog · eQSL · HRDLog	Uploads as you log, and confirmations back.
PSK Reporter	Your decodes go up as reception reports, and reports of your signal come back.
DX cluster · RBN	The spots feed the Needed board and the alerts, with VHF spots checked against receivers near you.
APRS-IS	The internet APRS feed, read-only, and a receive-only iGate.
CHIRP	CSV round trip, so channels move to and from roughly 1,000 radio models.

Setup, safety and platforms

	Detail
Setup	A four-step wizard that detects the radio, pairs its sound card and imports your log. Every step can be skipped and run again from Settings.
Transmit	TX is a switch you turn on; Nexus never keys up on its own. Your license class locks out every segment you cannot use, the 60 m channels included, and a watchdog stops a transmission left unattended for six minutes.
Launch	Nexus opens the radio read-only and commands nothing until you act, so a rig parked on 40 m LSB for a net stays there.
Updates	Signed and checked before they install. An update waits while you are transmitting, tuning, in a contact or calling CQ, and says which.
Crash reports	On Windows, a crash writes a report naming the component at fault. It records addresses and module names only: no callsign, no log and no personal information.
Accessibility	Works with JAWS and NVDA with nothing to switch on. Band Activity, the Call Roster and the Needed board are keyboard-navigable, and spoken decodes and a TX/RX tone are there if you want them.
Languages	English, German, Spanish, French and Japanese. Frequencies, callsigns, grids, reports and mode names are never translated: 14.074 is 14.074 in every language.
Platforms	Windows 10 and 11 (64-bit); macOS 12 or later on Apple Silicon, signed and notarized; Linux on a PC (Ubuntu 24.04 or newer), as a .deb or an AppImage; Raspberry Pi 3, 4 and 5 on 64-bit Raspberry Pi OS.

When nothing decodes

A dead band, a deaf receiver, the wrong sound card and a radio on the wrong frequency all look the same: silence. Nexus says which one it is.

Cause	What you see
Wrong frequency	The readout says where the radio is and where the mode lives (on 144.174 USB when APRS needs 144.390 FM, for example), with a Tune button that fixes it.
Squelch or sound card	A closed squelch (the receiver is alive, the level is zero) is reported apart from a sound card that delivers nothing, with the input level in dBFS so you can see what the decoder hears.
Rig or audio at setup	The Setup health strip shows whether the rig answers, whether receive audio arrives and whether TX works. Hover a light for the radio's own reply.

TempoFast and TempoDeep

Nexus carries two weak-signal modes of our own. TempoFast is a coherent 4-CPM mode on a four-second cycle with incremental-redundancy HARQ: when a decode fails, the next transmission adds new parity, and the receiver combines everything it holds until the message decodes. TempoDeep is a non-coherent 8-FSK mode on a 15-second cycle, for paths that fade.

Both have completed real contacts on the air, including a two-station QSO on 6 m. The thresholds below come from our simulations, and on-air reports are what will replace them. Both modes are plain text with a published specification.

A shorter cycle costs sensitivity. TempoFast gives up about 6 dB against FT8 for a cycle almost four times as fast, and its HARQ wins some of that back. Rings, marked (sim), are our simulations; dots are the published figures for FT4 and FT8. JS8 is not plotted: the spec gives it a 15 s cycle and no threshold of its own.

When a TempoFast decode fails, the next transmission carries 87 new parity bits, and the receiver combines them with what it already holds. After three transmissions it is decoding a rate 0.26 code. Which transmission is which rides on the Costas sync pattern, so it costs no extra bits.

	TempoFast	TempoDeep
Modulation	Coherent 4-CPM (h = 1/2, BT = 0.3)	Non-coherent 8-FSK
T/R cycle	4 s	15 s
Occupied bandwidth	about 42 to 67 Hz (estimated)	50 Hz
FEC	LDPC(174,91) + CRC-14	LDPC(174,91) + CRC-14
HARQ	Incremental redundancy, on by default	None
AWGN threshold	≈ −15 dB (sim)	≈ −18.6 dB (sim)
Fading penalty	Large (coherent)	≈ 3.7 dB (sim)

The full protocol write-up

What Nexus does not do

Other contests

Contest mode covers the contests listed above. The ARRL RTTY Roundup and the WW Digi contest are not in it yet; for those, keep N1MM Logger+, and Nexus will send it every contact.
Running a DXpedition

Nexus works a DXpedition as a Hound. It has no Fox role for running one.
Transmitting iGate

APRS traffic from the internet is never sent out on the air. That would key a radio with nobody at it, so it stays out for good.
Digital-voice programming

DMR, D-STAR and Fusion repeaters show in the repeater search with badges, so you know they are there, but Nexus does not program them.

Nexus 1.21.0

Windows · macOS · Linux · Raspberry Pi · GPL-3.0

Download Nexus 1.21.0