Ready Main radio
Audio CAT ARQ Busy RX
— kHz
S4 USB
Radio & Connection
TRX frequency: —
RX level — calibration
– CLIP
8-bit audio over CAT: peaks belong in the green band (40–80 %). Too low throws away real resolution, CLIP destroys the decode. Set the level on the radio (AF / volume) — digital gain does not help.
Test tone (tune / modulation check)
Keys the transmitter and sends a steady 1 kHz tone for 5 s at reduced power, over the same USB audio path as ARDOP — so it checks the tuner/PA and the modulation at once. ⚠ This transmits on your dial frequency: make sure it is clear and legal for you. A carrier stresses the PA thermally — run QRP rigs (tr)uSDX/QMX only briefly. Stops automatically after 5 s.
Winlink gateways · imported on 2026-08-07 · 462 channels
160m80m60m40m30m20m17m15m12m10mTop 10
CALLSIGN · BEARINGTRX/Dial kHzMODEDIST.
Received Messages
New Message
Outbox
Language
4FSK demodulator
SDFT tolerates sample-rate drift much better and is preset for the (tr)uSDX (whose sound card drifts). For TRX with a precise sound card (Icom, QMX) the more efficient Goertzel demodulator is preset. Reset to the matching default on every TRX selection; switch here if you have decode problems or unusual propagation conditions.
Winlink Account (Secure Login)
Location (for gateway distance & bearing)
Audio / Recording
(tr)uSDX nG — base setup via CAT
Applies to the (tr)uSDX nG from firmware 0.222 only. None of this is stored in the radio — after a power cycle its own saved values are back.
Decoder / Protocol
ARDOP Winlink by DL2MAN
This project stands on the shoulders of others. Our heartfelt thanks to everyone whose work made this client possible — Rick Muething (KN6KB) and the ardopcf team for ARDOP, Martin Hebnes Pedersen (LA5NTA) for wl2k-go, F6FBB for the forwarding protocol, Haruyasu Yoshizaki for LZHUF, the ARSFI for the Winlink network, and Guido (PE1NNZ) for the (tr)uSDX.
A complete ARDOP modem stack and Winlink client (B2F) running entirely in the browser — for QRP operation with (tr)uSDX, IC-705, IC-7300 and QMX. Project lead, protocol and architecture decisions, hardware and OTA testing: Manuel, DL2MAN. Implementation and programming: Claude (Anthropic).
Sources & Protocols Used

ARDOP — Amateur Radio Digital Open Protocol
Protocol specification and original implementation: Rick Muething, KN6KB.

ardopcf — C reference implementation of ARDOP, from which the modem and protocol stack was ported 1:1.
© 2014–2024 Rick Muething (KN6KB), John Wiseman (G8BPQ), Peter LaRue (AI7YN) · MIT license
github.com/pflarue/ardop

wl2k-go — Winlink framework for Go; reference for the B2F layer and LZHUF compression.
© 2014–2016 Martin Hebnes Pedersen (LA5NTA) · MIT license
github.com/la5nta/wl2k-go

B2F / FBB forwarding protocol
FBB protocol: Jean-Paul Roubelat, F6FBB. B2F reference implementation: paclink-unix (Nicholas S. Castellano, N2QZ, and others).

LZHUF compression
Original algorithm and code: Haruyasu Yoshizaki (1988). Maintained implementation: the JNOS developers.

Winlink / WL2K
The Winlink 2000 network is a project of the Amateur Radio Safety Foundation, Inc. (ARSFI).

CAT control
Icom CI-V command reference (IC-7300, IC-705) — © Icom Inc. (tr)uSDX and QMX are controlled via Kenwood-compatible CAT commands (TS-480).

Winlink gateway list
RMS channel list (ARDOP) from winlink.org/RMSChannels — ARSFI. Winlink Web Services API (api.winlink.org) as a research source for the update feature.

(tr)uSDX — target platform / transceiver.
DL2MAN (Manuel) and Guido, PE1NNZ.

License
MIT license. Free use, modification and redistribution as long as the copyright notices and license text are preserved. The copyright notices of ardopcf (Muething / Wiseman / LaRue) and wl2k-go (Pedersen) are listed above and included in full in the bundled LICENSE file.
Note
The client is officially registered with Winlink (client ID ARDOPCHROME). Our thanks go to the Winlink Development Team for the smooth collaboration on integrating the client — and for the care they take in safeguarding the interoperability of the Winlink network.
No warranty — disclaimer of liability
ARDOP Winlink is a voluntary, free-of-charge service, provided AS IS and without warranty of any kind — no guarantee that it works, decodes, connects or delivers mail, on any hardware, on any band, in any situation. To the maximum extent permitted by law, all liability for any damage or loss arising from the use of, or the inability to use, this software is excluded — emphatically including emergency and field use. HF propagation, radios, cables, browsers and operating systems fail; never make this client your only emergency channel, and always keep an independent fallback. You transmit under your own callsign, your own licence and your own responsibility. The bundled MIT licence states the same in legal form: “the software is provided ‘as is’, without warranty of any kind.”