WSJT (amateur radio software)


WSJT is a computer program used for weak-signal radio communication between amateur radio operators. The program was initially written by Joe Taylor, K1JT, but is now open source and is developed by a small team. The digital signal processing techniques in WSJT make it substantially easier for amateur radio operators to employ esoteric propagation modes, such as high speed meteor scatter and moonbounce.

History

WSJT was originally released in 2001 and has undergone several major revisions. Communication modes have been both added and removed from the software over the course of its development. Since 2005, the software has been released as open source software under the GNU General Public License. This licensing change required substantial rewrites and took several months to complete. Although Joe Taylor was the original developer, several programmers are currently involved in writing the software. Currently, the program is written in Python and C, with several utilities written in Fortran.
WSJT versions up through 7.06 r1933 and earlier were aggregations of previous versions, and as such WSJT7 contained 16 different modes. As of version 8.0 the available modes changed completely such that WSJT8 now offers 5 different modes -- none of which are back-compatible with WSJT7 or earlier releases. This backwards-incompatibility includes JT64A, such that the preview release of JT64A in WSJT7 cannot communicate with the stable release of JT64A in WSJT8., the latest WSJT version is WSJT10.

Communication modes provided

The software carries a general emphasis on weak-signal operation and advanced DSP techniques; however, the communication modes rely upon different ionospheric propagation modes and may be used on many different bands.
WSJT's communication modes can be divided into fast and slow modes. While fast modes send character-by-character without error correction, the slow modes aim to optimize for minimal QRO use. As of WSJT10, supported fast modes are JTMS, FSK441, ISCAT, and JT6M, and the slow modes are JT65 and JT4. WSJT-X 1.8 additionally implements the "slow" JT9, FT8, and QRA64. Some modes have derived submodes with larger tone spacing. Two other modes, WSPR and Echo are included for measuring propagation and testing moon bounce echo.

FSK441

FSK441, introduced in 2001 as the first communications mode included with WSJT, is designed to support communication using streaks of radio-reflecting ions created in the ionosphere by the trails of meteors entering the Earth's atmosphere. The bursts of signal created by such trails are commonly referred to as “pings”, due to their characteristic sound. Such pings may be as short as a tenth of a second and carry enough information to complete at least one stage of a contact. FSK441 employs multi-frequency shift keying using four tones, at a data rate of 441 baud. Because of the choice of character codes in the protocol, it is self-synchronizing and does not require an explicit synchronization tone. FSK441 is generally used on the 2-meter and 70-centimeter amateur bands. Contacts may be made at almost any time at distances of up to 1400 miles.
When transmitted messages include at least one space, the FSK441 decoding algorithm uses that space character as a syncword for zero-overhead synchronization.
Mode is no longer part of wsjt-x v.2.1.2.

JT6M

JT6M, introduced in late 2002, is intended for meteor scatter and other ionospheric scattering of signals, and is especially optimized for the 6-meter band. The mode also employs multiple frequency-shift keying, but at 44 tones. One of the tones is a synchronization tone, leaving 43 tones to carry data. The symbol rate is 21.53 baud; the actual data rate as encoded for transmit is 14.4 characters per second. The mode is known for sounding "a bit like piccolo music".
Mode is no longer part of wsjt-x v.2.1.2.

JT65

JT65, developed and released in late 2003, is intended for extremely weak but slowly varying signals, such as those found on troposcatter or Earth-Moon-Earth paths. It can decode signals many decibels below the noise floor in a 2500 Hz band, and can often allow amateurs to successfully exchange contact information without signals being audible to the human ear. Like the other modes, multiple-frequency shift keying is employed; unlike the other modes, messages are transmitted as units after being compressed and then encoded with a process known as forward error correction. The FEC adds redundancy to the data, such that all of a message may be successfully recovered even if some bits are not received by the receiver. Because of this FEC process, messages are either decoded correctly or not decoded at all, with very high probability. After messages are encoded, they are transmitted using MFSK with 65 tones.
Operators have also begun using the JT65 mode for contacts on the HF bands, often using QRP ; while the mode was not originally intended for such use, its popularity has resulted in several new features being added to WSJT in order to facilitate HF operation.

JT9

JT9, intended for MF and HF use, was introduced in an experimental version of WSJT, known as WSJT-X. It uses the same logical encoding as JT65, but modulates to a 9-FSK signal. With 1-minute transmission intervals, JT9 occupies less than 16 Hz bandwidth. JT9 also has versions designed for longer transmission intervals of 2 minutes, 5 minutes, 10 minutes or 30 minutes. These extended versions take increasingly less bandwidth and permit reception of even weaker signals.

FT8

Joe Taylor, K1JT, announced on June 29, 2017 the availability of a new mode in the WSJT-X software, FT8. FT8 stands for "Franke-Taylor design, 8-FSK modulation" and was created by Joe Taylor, K1JT and Steve Franke, K9AN. It is described as being designed for "multi-hop Es where signals may be weak and fading, openings may be short, and you want fast completion of reliable, confirmable QSO's".
According to Taylor, the important characteristics of FT8 are —
Compared to the so-called "slow modes", FT8 is a few decibels less sensitive, but allows completion of QSOs four times faster. Bandwidth is greater than JT9, but about one-quarter of JT65A and less than one-half of QRA64. Compared with the "fast modes", FT8 is significantly more sensitive, has much narrower bandwidth, uses the vertical waterfall, and offers multi-decoding over the full displayed passband. Features not yet implemented include signal subtraction, two-pass decoding, and use of a priori information as it accumulates during a QSO."

FT4

In 2019, Taylor, et al, introduced FT4, an experimental protocol which is similar to FT8 but has a shorter T/R sequence length for faster contest exchanges.

Alternative software for JT65

There are alternative software packages available for JT65 including MultiPSK, and JT65-HF HB9HQX Edition. The JT65-HF HB9HQX Edition software, along with the source code, may be obtained from Sourceforge.
An article series on using the original JT65-HF software appeared in CQ Amateur Radio's October & November 2010 issues. And MSHV from LZ2HV recompiled from source code of WSJT-X with different GUI implementation both for Linux and Windows OS.