WSJT (amateur radio software)

WSJT (amateur radio software)
Name	WSJT
Caption	WSJT-X, the modern implementation of the WSJT software suite
Developer	K1JT
Released	0 2001
Latest release version	2.7.1
Latest release date	15 December 2024
Programming language	Fortran, C++
Operating system	Microsoft Windows, Linux, macOS
Genre	Amateur radio software
License	GNU General Public License
Website	https://physics.princeton.edu/pulsar/k1jt/wsjtx.html

WSJT (amateur radio software) is a suite of computer programs used by amateur radio operators for weak-signal communication. Developed by Nobel laureate Joe Taylor, K1JT, the software enables reliable contacts over long distances using very low power and compromised antennas. It employs sophisticated digital signal processing techniques to decode signals far below the noise floor, facilitating modes like FT8, which has become immensely popular worldwide.

Overview

The WSJT suite, with its flagship implementation WSJT-X, is designed for specialized amateur radio communications on the HF, VHF, UHF, and microwave bands. It facilitates communication under challenging conditions, such as during meteor scatter, moonbounce (Earth-Moon-Earth), and transequatorial propagation. The software's core innovation is its ability to extract extremely weak signals from background noise using advanced Forward error correction and efficient protocols. This capability has revolutionized activities like contesting and DXing, allowing operators to make contacts that were previously impractical with traditional single-sideband modulation or Morse code.

History and development

The original WSJT software was created by Joe Taylor, a professor of astrophysics at Princeton University and recipient of the Nobel Prize in Physics for his work on binary pulsars. First released publicly in 2001, its development was driven by Taylor's interest in VHF amateur radio and the challenges of weak-signal propagation. Early versions focused on modes for meteor scatter and moonbounce. The project evolved significantly with the release of WSJT-X, a complete rewrite in C++ led by a team including K9AN and G4WJS. Major milestones include the introduction of the JT65 protocol, later superseded by the faster and more efficient FT8 mode, which sparked a global resurgence in HF amateur radio activity.

Modes of operation

The software supports multiple digital modes, each optimized for specific propagation conditions and purposes. The foundational JT65 mode, designed for moonbounce and extreme weak-signal work, uses one-minute transmit/receive sequences. JT9 is a narrower-bandwidth alternative to JT65 for HF use. The revolutionary FT8 mode, introduced in 2017, features 15-second cycles and has become the dominant digital mode for HF and VHF weak-signal communication. Other specialized modes include MSK144 for meteor scatter, Q65 for general weak-signal work, and WSPR (Weak Signal Propagation Reporter), a beacon mode for propagation research. Each mode employs specific combinations of Forward error correction, interleaving, and modulation, such as Frequency-shift keying.

Technical principles

WSJT software operates on principles of robust digital communication and Digital signal processing. It uses highly structured messages with strong Forward error correction, typically Low-density parity-check codes, to correct errors caused by noise and fading. Signals are modulated using very narrow-band Frequency-shift keying or Gaussian frequency-shift keying. The software performs synchronized transmission and reception in strict, pre-defined time slots, allowing coherent signal averaging at the receiver. A critical component is the Fast Fourier transform-based decoder, which identifies signal presence, frequency, and decodes the message from a waterfall display. This process allows decoding of signals with a signal-to-noise ratio as low as -20 dB or more in some modes.

Typical uses and applications

The primary use is for making two-way contacts in challenging weak-signal scenarios on the amateur radio bands. This includes DXing to rare entities, moonbounce communication via the Moon, and exploiting brief meteor scatter openings on the VHF bands. The WSPR mode is widely used for passive propagation research, with a global network of beacons mapping real-time band conditions. The software is also integral to amateur radio contesting, particularly in events like the ARRL International EME Contest. Furthermore, it serves an educational role in demonstrating advanced Digital signal processing and radio propagation principles to students and enthusiasts.

Software implementation and requirements

The modern WSJT-X application is written primarily in C++ and uses the Qt framework for its cross-platform graphical user interface. It relies on external libraries such as FFTW for Fourier transforms and Hamlib for transceiver control. The software is open-source, distributed under the GNU General Public License, and is compiled for Microsoft Windows, Linux, and macOS operating systems. System requirements are modest, needing a standard PC with a sound card interface to the radio. It interfaces with transceivers via CAT control protocols and requires precise computer clock synchronization, often achieved using Network Time Protocol software, to maintain the strict timing essential for its modes.

Category:Amateur radio software Category:Free software