WSJT-X User Guide

We include screen shots that illustrate many of the settings and features of WSJT-X. Keep in mind that WSJT-X is a multi-platform application: the detailed appearance of windows and user controls may be significantly different in Windows, Linux, or macOS environments. The underlying functionality is the same on all operating systems, however. Where desirable we call special attention to important platform differences.

In this manual the following icons call attention to particular types of information:

The WSJT-X user interface (UI) is now available in many languages. When a translated UI is available for the computer’s default System Language, it will appear automatically on program startup. The UI language may be overridden if desired by starting WSJT-X with a command line option. For example, to start WSJT-X with its user interface in Spanish, enter this command at the prompt:

wsjtx --language es

WSJT-X is part of an open-source project released under the GNU General Public License (GPLv3). If you have programming or documentation skills or would like to contribute to the project in other ways, please make your interests known to the development team. We especially encourage those with translation skills to volunteer their help, either for this User Guide or for the program’s user interface.

The project’s source-code repository can be found at SourceForge, and communication among the developers takes place on the email reflector wsjt-devel@lists.sourceforge.net. Bug reports and suggestions for new features, improvements to the WSJT-X User Guide, etc., may be sent there as well. You must join the group before posting to the email list.

Before using WSJT-X, please read our licensing terms here.

Download and execute the package file wsjtx-2.6.1-win32.exe (Windows 7 or later, 32-bit) or wsjtx-2.6.1-win64.exe (Windows 7 or later, 64-bit) following these instructions:

C:\Users\<username>\AppData\Local\WSJT-X.

Debian, Ubuntu, and other Debian-based systems including Raspberry Pi OS:

You may also need to execute the following command in a terminal:

Fedora, CentOS, Red Hat, and other rpm-based systems:

You may also need to execute the following command in a terminal:

macOS10.13 and later: Download the file wsjtx-2.6.1-Darwin.dmg to your desktop, double-click it and consult its ReadMe file for important installation notes.

If you have already installed a previous version, you can retain it by changing its name in the Applications folder (such as from WSJT-X to WSJT-X_2.2). You can then proceed to the installation phase.

Take note also of the following:

Select the General tab on the Settings window. Under Station Details enter your callsign, grid locator (preferably the 6-character locator) and IARU Region number. Region 1 is Europe, Africa, the Middle East, and Northern Asia; Region 2 the Americas; and Region 3 Southern Asia and the Pacific. This information will be sufficient for initial tests.

Meanings of remaining options on the General tab should be self-explanatory after you have made some QSOs using WSJT-X. You may return to set these options to your preferences later.

WSJT-X offers CAT (Computer Aided Transceiver) control of relevant features of most modern transceivers. To configure the program for your radio, select the Radio tab.

When all required settings have been made, click Test CAT to test communication between WSJT-X and your radio. The button should turn green to indicate that proper communication has been established. Failure of the CAT-control test turns the button red and displays an error message. After a successful CAT test, toggle the Test PTT button to confirm that your selected method of T/R control is working properly, the button turns red if the rig has been successfully keyed. (If you selected VOX for PTT Method, you can test T/R switching later by using the Tune button on the main window.)

Select the Audio tab to configure your sound system.

Tx Macros are an aid for sending brief, frequently used free-text messages such as the examples shown below.

Programs like JTAlert use the UDP Server feature to obtain information about running WSJT-X instances. If you are using JTAlert to control WSJT-X, be sure to check the Accept UDP requests box.

By default, the Working Frequencies table contains a list of frequencies conventionally used for modes FT8, JT4, JT9, JT65, MSK144, WSPR, and Echo. Conventions may change with time or by user preference; you can modify the frequency table as desired.

Other more advanced maintenance operations are available on the right-click context popup menu that should be self-explanatory.

Frequency Calibration: If you have calibrated your radio using WWV or other reliable frequency references, or perhaps with the technique described in Accurate Frequency Measurements with your WSPR Setup, enter the measured values for Intercept A and Slope B in the equation

where “Dial error” and A are in Hz, f is frequency in MHz, and B is in parts per million (ppm). Frequency values sent to the radio and received from it will then be adjusted so that frequencies displayed by WSJT-X are accurate.

Station Information: You can save Band, Offset and Antenna Description information for your station. The antenna information will be included in reception reports sent to PSK Reporter. By default the frequency offset for each band is zero. Nonzero offsets may be added if (for example) a transverter is in use.

Stations who are known to have uploaded their logs to the ARRL LoTW QSL matching service can be highlighted. The data used to determine this is available online.

JT65 VHF/UHF/Microwave decoding parameters

Miscellaneous

Special Operating Activity

An optional Dark style is available. To make it effective you will probably want to redefine your color settings. In Windows or Linux, start the program from a command-prompt window using the following command, or modify the WSJT-X desktop shortcut accordingly:

In macOS, enter the following command from a terminal:

In Linux using the Unity or GNOME GUI the following commands will update the WSJT-X start up:

Depending on your operating system, the main WSJT-X window will look something like this:

The following steps will download sample audio Wave files that were originally recorded by WSJT-X. These files can be read in and processed by WSJT-X to simulate realtime operation.

The WSJT-X Wide Graph window displays the frequency spectrum of the received audio. Usually, the upper portion of the window shows a waterfall plot of the frequency spectrum (a spectrogram) and a line plot of the current or average spectrum. Controls at the bottom of the window are used to set up the displayed audio frequency range, color palette, and scaling of the spectrum displays. A control on the bottom right of the Wide Graph (displayed as Spec nn%) lets you control the vertical fraction of the window occupied by the spectrum line plot. It is important to set appropriate lower and upper audio frequency limits for the Wide Graph because these limits define the FT8 decoder’s search window. For this tutorial, the limits will be set to cover 100-3300 Hz:

The N Avg setting controls how many spectra are averaged to produce each line in the spectrogram. Smaller values make the spectrogram update more frequently, resulting in signals being more spread out in the vertical (time) direction. On the other hand, larger values make it easier to detect very weak signals:

The Palette setting controls the color scheme used for the spectrogram:

When Flatten is checked, WSJT-X attempts to correct for slope or curvature in the receiver’s passband shape.

The line plot can be set to display the current (un-averaged) spectrum or the cumulative (averaged) spectrum:

The Spec nn% setting determines what fraction of the vertical extent of the Wide Graph will be used for the line plot of the spectrum. Setting Spec to 0 will eliminate the line plot and a setting of 100 will eliminate the spectrogram and show only the line plot:

Decoding takes place at the end of a receive sequence. With Decode set to Deep, three decoding passes will be done and the Decode button on the mainwindow will illuminate three times, once for each pass. The first decoding attempt in each decoding pass is done at the selected Rx frequency, indicated by the U-shaped green marker on the waterfall frequency scale. All decodes appear in the left (Band Activity) window. The right (Rx Frequency) text window displays any decodes obtained at the current Rx frequency along with any decodes addressed to My Call (K1JT in this case). The red marker on the waterfall scale indicates your Tx frequency.

Twenty-one FT8 signals are decoded from the example file. The number of decodes is shown in a box at the bottom of the main window. When this file was recorded HA5WA was finishing a QSO with K1JT, and his 73 message is shown in red because it is addressed to My Call (in this case K1JT). By default, lines containing CQ are highlighted in green, and lines with My Call (K1JT) in red. Notice that K1JT has two callers; HA0DU and EA3AGB.

To gain some feeling for controls frequently used when making QSOs, try double-clicking with the mouse on the decoded text lines and on the waterfall spectral display. You should be able to confirm the following behavior:

This special operating mode enables DXpeditions to make FT8 QSOs at very high rates. Both stations must use WSJT-X Version 1.9 or later. Detailed operating instructions for FT8 DXpedition Mode are available online. Do not try to use DXpedition mode without reading these instructions carefully!

FT4 is designed for contesting, particularly on the HF bands and 6 meters. Compared with FT8 it is 3.5 dB less sensitive and requires 1.6 times the bandwidth, but it offers the potential for twice the QSO rate.

The FT4 user interface includes a button labeled Best S+P.

Clicking Best S+P during an Rx cycle arms the program to examine all CQ messages decoded at the end of the Rx sequence. The program will select the best potential QSO partner (from a contesting perspective), and treat it as if you had double-clicked on that line of decoded text. Here "best potential QSO partner" means "New Multiplier" (1st priority) or "New Call on Band" (2nd priority). "New Multiplier" is currently interpreted to mean "New DXCC"; a more broadly defined multiplier category (for the FT Roundup rules) will be implemented in due course. We may provide additional priority rankings, for example “New Grid on Band” (useful for North American VHF contests), sorting by signal strength, etc.

Best S+P is a useful feature only if you have defined what "best" is supposed to mean. This is done by configuring suitable options on the Settings | Colors tab. Selection and ordering of color-highlighting options determines what potential QSO partners will be chosen by the "Best S+P" feature. Optimum choices will be different for different contests. In a contest using FT Roundup rules we recommend activating My Call in message, New DXCC, New Call on Band, CQ in message and Transmitted message, reading from top to bottom.

Do not confuse FST4 with FT4, which has a very different purpose! FST4 is designed primarily for making weak-signal 2-way QSOs on the LF and MF bands. T/R periods from 15 s up to 1800 s are available. Longer T/R periods provide better sensitivity only if Tx and Rx frequency instability and channel Doppler spread are small enough so that received signals remain phase coherent over periods spanning several transmitted symbols. Generally speaking, Rx and Tx frequency changes during the transmission and channel Doppler spread should each be small compared to the symbol keying rate shown for each T/R duration in Table 7 within section Protocol Specifications. For example, the keying rate for the 1800 s T/R period is 0.089 Baud, so successful operation using this T/R length requires Tx and Rx frequency stability better than 0.089 Hz over the duration of the 1800 s transmission in addition to channel Doppler spread smaller than 0.089 Hz.

Operation with FST4 is similar to that with other WSJT-X modes: most on-screen controls, auto-sequencing, and other features behave in familiar ways. However, operating conventions on the 2200 and 630 m bands have made some additional user controls desirable. Spin boxes labeled F Low and F High set lower and upper frequency limits used by the FST4 decoder, and these limits are marked by dark green angle-bracket symbols < > on the Wide Graph frequency scale:

It’s best to keep the decoding range fairly small, since QRM and transmissions in other modes or sequence lengths will slow down the decoding process (and of course will be undecodable). By checking Single decode on the File | Settings | General tab, you can further limit the decoding range to the setting of F Tol on either side of Rx Freq.

A noise blanker can be enabled by setting the NB percentage to a non-zero value. This setting determines how many of the largest-amplitude samples will be blanked (zeroed) before the data is submitted to the decoder. Most users find that settings between 0% (no blanking) and 10% work best. If the noise blanker percentage is set to -1%, then the decoder will try 0, 5, 10, 15, and 20 % in succession. Similarly, a setting of -2% causes the decoder to loop over blanking percentages 0, 2, 4, …​ 20 %. To save time, the multiple blanking percentages triggered by negative NB settings are tried only for signal candidates located near (within +/- 20 Hz) of the Rx frequency setting.

FST4W is used in the same way as WSPR, but FST4W has significant advantages for use on the 2200 m and 630 m bands. By default the central Rx Freq is 1500 Hz and F Tol is 100 Hz, so the active decoding range is 1400 to 1600 Hz. However, for added flexibility you can select different center frequencies and F Tol values. We expect that usage conventions will soon be established for FST4W activity on 2200 and 630 m.

A new drop-down control below F Tol offers a round-robin mode for scheduling FST4W transmissions:

If three operators agree in advance to select the options 1/3, 2/3, and 3/3, for example, their FST4W transmissions will occur in a fixed sequence with no two stations transmitting simultaneously. Sequence 1 is the first sequence after 00:00 UTC. For WSPR-like scheduling behavior, you should select Random with this control.

Note that the weak signal associated with the single decode is all but invisible on the widegraph spectrogram.

By longstanding tradition, a minimally valid QSO requires the exchange of callsigns, a signal report or some other information, and acknowledgments. WSJT-X is designed to facilitate making such minimal QSOs using short, structured messages. The process works best if you use these formats and follow standard operating practices. The recommended basic QSO goes something like this:

Standard messages consist of two callsigns (or CQ, QRZ, or DE and one callsign) followed by the transmitting station’s grid locator, a signal report, R plus a signal report, or the final acknowledgements RRR or 73. These messages are compressed and encoded in a highly efficient and reliable way. In uncompressed form (as displayed on-screen) they may contain as many as 22 characters. Some operators prefer to send RR73 rather than RRR. This is workable because RR73 is encoded as a valid grid locator, one unlikely ever to be occupied by an amateur station.

Signal reports are specified as signal-to-noise ratio (S/N) in dB, using a standard reference noise bandwidth of 2500 Hz. Thus, in the example message above, K1ABC is telling G0XYZ that his signal is 19 dB below the noise power in bandwidth 2500 Hz. In the message at 0004, G0XYZ acknowledges receipt of that report and responds with a –22 dB signal report. JT65 reports are constrained to lie in the range –30 to –1 dB, and values are significantly compressed above about -10 dB. JT9 supports the extended range –50 to +49 dB and assigns more reliable numbers to relatively strong signals.

Users often add some friendly chit-chat at the end of a QSO. Free-format messages such as “TNX ROBERT 73” or “5W VERT 73 GL” are supported, up to a maximum of 13 characters, including spaces. In general you should avoid the character / in free-text messages, as the program may then try to interpret your construction as part of a compound callsign. It should be obvious that the JT4, JT9, and JT65 protocols are not designed or well suited for extensive conversations or rag-chewing.

The T/R cycles of many WSJT-X modes allow only a few seconds to inspect decoded messages and decide how to reply. Often this is not enough time, so for FST4, FT4, FT8, MSK144, and Q65 the program offers a basic auto-sequencing feature.

Check Auto Seq on the main window to enable this feature:

When calling CQ you may choose to select CQ: First to reply automatically to the first decoded responder, or CQ: Max Dist to reply to the most distant responder.

The FT4, FT8, and MSK144 protocols support special messages optimized for NA VHF and EU VHF contests. FT4 and FT8 also support messages for ARRL Field Day, FT Roundup, and the WW Digi contest. The decoders recognize and decode these messages at any time. Configure the program to automatically generate the required message types for contest exchanges and carry out suitable auto-sequencing by selecting a supported operating activity on the Settings | Advanced tab. Model QSOs then proceed as follows, for each event type:

NA VHF Contest and ARRL International Digital Contest

Either callsign (or both) may have /R appended to signify a Rover in a VHF contest. You can use RR73 in place of RRR, and the final 73 is optional.

EU VHF Contest

Either callsign (or both) may have /P appended.

ARRL Field Day

FT Roundup

WW Digi Contest

Contest QSOs are generally treated as invalid when they appear in one station’s log and not the supposed QSO partner’s. To avoid Not-in-Log (NIL) penalties for yourself and others, we recommend the following guidelines for contest logging with FT4, FT8, and MSK144:

Modes with 77-bit message payloads: FST4, FT4, FT8, MSK144, and Q65

Compound callsigns like PJ4/K1ABC or K1ABC/3 and special event callsigns like YW18FIFA are supported for normal QSOs but not for contest-style messages. Model QSOs look something like this:

The compound or nonstandard callsigns are automatically recognized and handled using special message formats. One such callsign and one standard callsign may appear in most messages, provided that one of them is enclosed in < > angle brackets. If the message includes a grid locator or numerical signal report, the brackets must enclose the compound or nonstandard callsign; otherwise the brackets may be around either call.

Angle brackets imply that the enclosed callsign is not transmitted in full, but rather as a hash code using a smaller number of bits. Receiving stations will display the full nonstandard callsign if it has been received in full in the recent past. Otherwise it will be displayed as < . . . >. These restrictions are honored automatically by the algorithm that generates default messages for minimal QSOs. Except for the special cases involving /P or /R used in VHF contesting, WSJT-X 2.6 offers no support for two nonstandard callsigns to work each other.

Modes with 72-bit message payloads: JT4, JT9, and JT65

In the 72-bit modes, compound callsigns are handled in one of two possible ways:

A list of about 350 of the most common prefixes and suffixes can be displayed from the Help menu. A single compound callsign involving one item from this list can be used in place of the standard third word of a message (normally a locator, signal report, RRR, or 73). The following examples are all acceptable messages containing Type 1 compound callsigns:

The following messages are not valid, because a third word is not permitted in any message containing a Type 1 compound callsign:

A QSO between two stations using Type 1 compound-callsign messages might look like this:

Notice that the full compound callsign is sent and received in the first two transmissions. After that, the operators omit the add-on prefix or suffix and use the standard structured messages.

Prefixes and suffixes not found in the displayable short list are handled by using Type 2 compound callsigns. In this case the compound callsign must be the second word in a two- or three-word message, and the first word must be CQ, DE, or QRZ. Prefixes can be 1 to 4 characters, suffixes 1 to 3 characters. A third word conveying a locator, report, RRR, or 73 is permitted. The following are valid messages containing Type 2 compound callsigns:

In each case, the compound callsign is treated as Type 2 because the add-on prefix or suffix is not one of those in the fixed list. Note that a second callsign is never permissible in these messages.

QSOs involving Type 2 compound callsigns might look like either of the following sequences:

Operators with a compound callsign use its full form when calling CQ and possibly also in a 73 transmission, as may be required by licensing authorities. Other transmissions during a QSO may use the standard structured messages without callsign prefix or suffix.

Before attempting your first QSO with one of the WSJT modes, be sure to go through the Basic Operating Tutorial above as well as the following checklist:

To activate the VHF-and-up features:

The main window will reconfigure itself as necessary to display controls supporting the features of each mode.

Five different types of Doppler tracking are provided:

JT4 is designed especially for EME on the microwave bands, 2.3 GHz and above.

The following screen shot shows one transmission from a 10 GHz EME QSO using submode JT4F.

In many ways JT65 operation on VHF and higher bands is similar to HF usage, but a few important differences should be noted. Typical VHF/UHF operation involves only a single signal (or perhaps two or three) in the receiver passband. We recommend that you check Single decode on the Settings → General tab, and do not check Two pass decoding on the Advanced tab. With VHF features enabled the JT65 decoder will respond to special message formats often used for EME: the OOO signal report and two-tone shorthand messages for RO, RRR, and 73. These messages are always enabled for reception; they will be automatically generated for transmission if you check the shorthand message box Sh. Deep on the Decode menu will be automatically selected. You may optionally include Enable averaging, Enable Deep search, and Enable AP.

The following screen shot shows three transmissions from a 144 MHz EME QSO using submode JT65B and shorthand messages. Take note of the colored tick marks on the Wide Graph frequency scale. The green marker at 1220 Hz indicates the selected QSO frequency (the frequency of the JT65 Sync tone) and the F Tol range. A green tick at 1575 Hz marks the frequency of the highest JT65 data tone. Orange markers indicate the frequency of the upper tone of the two-tone signals for RO, RRR, and 73.

Q65 is designed for fast-fading signals: tropospheric scatter, rain scatter, ionospheric scatter, trans-equatorial propagation (TEP), EME, and the like. The following screen shot shows a series of ionospheric scatter QSOs using submode Q65-30A on the 6 meter band. The received signals were barely audible most of the time.

The Q65 decoder takes advantage of a priori (AP) information such as the encoded forms of one’s own callsign and the message word CQ. In normal usage, as a QSO progresses AP information increases to include the callsign of the station being worked and perhaps his/her 4-digit grid locator. The decoder takes advantage of whatever AP information is currently available.

For Q65 EME QSOs on the microwave bands, some operators use short-form messages consisting of a single tone. To activate automatic generation of these messages, check the box labeled Sh. This also enables the generation of a single tone at 1000Hz by selecting Tx6, to assist in finding signals initially. The box labeled Tx6 switches the Tx6 message from 1000Hz to 1250Hz to indicate to the other station that you are ready to receive messages. These short-form messages are not decoded automatically, and auto-sequencing will not respond to them. You must recognize and interpret them yourself.

Meteor scatter QSOs can be made any time on the VHF bands at distances up to about 2100 km (1300 miles). Completing a QSO takes longer in the evening than in the morning, longer at higher frequencies, and longer at distances close to the upper limit. But with patience, 100 W or more, and a single yagi it can usually be done. The following screen shot shows two 15-second reception intervals containing MSK144 signals from three different stations.

Unlike other WSJT-X modes, the MSK144 decoder operates in real time during the reception sequence. Decoded messages will appear on your screen almost as soon as you hear them.

To configure WSJT-X for MSK144 operation:

Echo mode provides tools for two types of measurements: echoes of your transmitted signal from the Moon, and broadband noise power received from the Sun, Moon, and possibly other sources including nearby ground. In each case the system noise temperature (noise power referred to the antenna terminals, expressed in Kelvin degrees) serves as the reference noise level. Such measurements are widely used for optimizing a station’s capabilities for Earth-Moon-Earth (EME) communication.

For lunar echoes, WSJT generates short fixed-frequency transmissions that alternate with reception intervals at the appropriate Doppler-shifted frequency. With Split Operation set to Rig or Fake It on the Settings | Radio tab, check Doppler tracking and Own Echo on the Astronomical Data window. Point your antenna at the Moon and click Enable Tx on the main window to start a sequence of echo measurements. Each cycle takes 6 seconds. If strong enough, echoes will be visible in the waterfall. Their average spectrum will be displayed in the Echo Graph window, and numerical parameters of the measurements appear in the main window:

At the end of each echo cycle a line of data in the main text window displays the following information:

Until the advent of Q65, digital EME has mostly been done using JT65A on the 50 MHz band, JT65B on 144 and 432 MHz, and JT65C on 1296 MHz. On higher microwave bands typical choices have been JT65C, one of the wider JT4 submodes, or QRA64, depending on the expected amount of Doppler spread. We now recommend a suitable submode of Q65 (which has replaced QRA64) for EME on any VHF or higher band: for example, Q65-60A on 50 and 144 MHz, Q65-60B on 432 MHz, Q65-60C on 1296 MHz, and Q65-60D on 10 GHz.

JT4, JT65, and Q65 offer Message Averaging — the summation of subsequent transmissions that convey the same message — to enable decodes at signal-to-noise ratios several dB below the threshold for single transmissions. JT4 and JT65 also allow Deep Search decoding, in which the decoder hypothesizes messages containing known or previously decoded callsigns and tests them for reliability using a correlation algorithm. JT65 and Q65 offer a priori (AP) decoding, which takes advantage of naturally accumulating information during a QSO.

For CW mode on SHF and microwave EME WSJT-X can be used to do Doppler shift correction if desired:

WSPR mode allows those with CAT-controlled radios to investigate propagation on many bands without user intervention. Coordinated hopping enables a sizable group of stations around the world to move together from band to band, thereby maximizing the chances of identifying open propagation paths.

The following screen shot is an example of WSPR operation with band hopping enabled:

A careful look at the screen shot above illustrates some of the impressive capabilities of the WSPR decoder. For example, look at the decodes at UTC 0152, 0154, and 0156 along with the corresponding minutes from the waterfall display below. Yellow ovals have been added to highlight two isolated signals decoded at -28 and -29 dB in the first and third two-minute interval. At 0154 UTC signals from VE3FAL, AB4QS, and K5CZD fall within a 5 Hz interval near audio frequency 1492 Hz; similarly, K3FEF, DL2XL/P, and LZ1UBO fall within a 6 Hz interval near 1543 Hz. Each of the overlapping signals is decoded flawlessly.

Menus at top of the main window offer many options for configuration and operation. Most of the items are self-explanatory; a few additional details are provided below. Keyboard shortcuts for some frequently used menu items are listed at the right edge of the menu.

The following controls appear just under the decoded text windows on the main screen. Some of them are visible only in certain modes.

Controls related to frequency selection, received audio level, the station being called, and date and time are found in the lower, left-hand section of the main window. Buttons are provided for making quick changes among the modes FT8, FT4, MSK144, Q65, and JT65, and for toggling FT8 Hound mode ON or OFF.

At the center of the main window are a number of controls used when making QSOs. Controls not relevant to a particular mode or submode may be "grayed out" (disabled) or removed from the display.

Controls familiar to users of program WSJT appear on Tab 1, providing six fields for message entry. Pre-formatted messages for the standard minimal QSO are generated when you click Generate Std Msgs or double-click on an appropriate line in one of the decoded text windows.

A Status Bar at the bottom edge of the main window provides useful information about operating conditions.

Labels on the Status Bar display such information as the program’s current operating state, configuration name, operating mode, and the content of your most recent transmitted message. The first label (operating state) can be Receiving, Tx (for Transmitting), Tx: Tune, or the name of the file opened from the File menu. This label is highlighted in green for Receiving, yellow for Tx, red for Tune, and light blue for a file name. When transmitting, the Tx message is displayed exactly as it will be decoded by receiving stations. The second label (as shown above) will be absent if you are using the Default setting on the Configurations menu. A progress bar shows the elapsed fraction of a Tx or Rx sequence. Finally, if the Watchdog (WD) timer was enabled on the Files | Settings | General tab, a label in the lower right-hand corner displays the number of minutes remaining before timeout.

The following controls appear at the bottom of the Wide Graph window. Decoding occurs only in the displayed frequency range; otherwise, controls on the Wide Graph window have no effect on the decoding process.

The waterfall palette used for the Fast Graph is the same as the one selected on the Wide Graph. Three sliders at the bottom of the Fast Graph window can be used to optimize gain and zero-offset for the displayed information. Hover the mouse over a control to display a tip reminding you of its function. Clicking the Auto Level button produces reasonable settings as a starting point.

The following controls appear at the bottom of the Echo Graph:

Most windows can be resized as desired. If you are short of screen space you can make the Main Window and Wide Graph smaller by hiding some controls and labels. To enable this feature uncheck the box labeled Controls at top left of the Wide Graph window, or the box Menus to the right of the Tune button on the Main Window.

The WSJT-X decoders for FST4, FT4, FT8, JT65, and Q65 include procedures that use naturally accumulating information during a minimal QSO. This a priori (AP) information increases sensitivity of the decoder by up to 4 dB, at the cost of a slightly higher rate of false decodes. AP is optional in FT8 and JT65, but is always enabled for Q65 and for FT4 and FST4 when decode depth is Normal or Deep.

For example: when you decide to answer a CQ, you already know your own callsign and that of your potential QSO partner. The software therefore “knows” what might be expected for at least 57 message bits (28 for each of two callsigns, one or more for message type) in the next received message. The decoder’s task is thus reduced to determining the remaining 15 bits of the message and ensuring that the resulting solution is reliable.

AP decoding starts by setting AP bits to the hypothesized values, as if they had been received correctly. We then determine whether the remaining message and parity bits are consistent with the hypothesized AP bits, with a specified level of confidence. Successful AP decodes are labeled with an end-of-line indicator of the form aP, where P is one of the single-digit AP decoding types listed in Table 1. For example, a2 indicates that the successful decode used MyCall as hypothetically known information. Type a7, used only in FT8 mode, uses information from the previous Rx sequence.

If a codeword is found that is judged to have high (but not overwhelmingly high) probability of being correct, a ? character is appended when the decoded message is displayed. To avoid misleading spots of occasional false decodes, messages so marked are not forwarded to PSK Reporter.

Table 2 lists the six possible QSO states that are tracked by the WSJT-X auto-sequencer, along with the type of AP decoding that would be attempted in each state in FT4 or FT8. The FST4 table (not shown) is the same except that it omits the decoding attempts for AP types 4 and 5 to save time.

Decoding with a priori information behaves slightly differently in JT65. Some details are provided in Tables 3 and 4.

Displayed information accompanying decoded messages generally includes UTC, signal-to-noise ratio in dB, time offset DT in seconds, and audio frequency in Hz. Some modes include additional information such as frequency offset from nominal (DF), frequency drift (Drift or F1), or distance (km or mi).

There may also be some cryptic characters with special meanings summarized in the following Table:

Many WSJT-X capabilities depend on signal-detection bandwidths of no more than a few Hz. Frequency accuracy and stability are therefore unusually important. We provide tools to enable accurate frequency calibration of your radio, as well as precise frequency measurement of on-the-air signals. The calibration procedure works by automatically cycling your CAT-controlled radio through a series of preset frequencies of carrier-based signals at reliably known frequencies, measuring the error in dial frequency for each signal.

You will probably find it convenient to define and use a special Configuration dedicated to frequency calibration. Then complete the following steps, as appropriate, for your system.

With modern synthesized radios, small measured offsets from 1500 Hz will exhibit a straight-line dependence on frequency. You can approximate the calibration of your radio by simply dividing the measured frequency offset (in Hz) at the highest reliable frequency by the nominal frequency itself (in MHz). For example, the 20 MHz measurement for WWV shown above produced a measured tone offset of 24.6 Hz, displayed in the WSJT-X decoded text window. The resulting calibration constant is 24.6/20=1.23 parts per million. This number may be entered as Slope on the File | Settings | Frequencies tab.

A more precise calibration can be effected by fitting the intercept and slope of a straight line to the whole sequence of calibration measurements, as shown for these measurements in the graph plotted below. Software tools for completing this task are included with the WSJT-X installation, and detailed instructions for their use are available at https://wsjt.sourceforge.io/FMT_User.pdf.

Using these tools and no specialized hardware beyond your CAT-interfaced radio, you can calibrate the radio to better than 1 Hz and compete very effectively in the ARRL’s periodic Frequency Measuring Tests.

After running Execute frequency calibration cycle at least once with good results, check and edit the file fmt.all in the log directory and delete any spurious or outlier measurements. The line-fitting procedure can then be carried out automatically by clicking Solve for calibration parameters on the Tools menu. The results are displayed as in the following screen shot. Estimated uncertainties are included for slope and intercept; N is the number of averaged frequency measurements included in the fit, and StdDev is the root mean square deviation of averaged measurements from the fitted straight line. If the solution seems valid, you are offered an Apply button to push that automatically sets the calibration parameters in File | Settings | Frequencies | Frequency Calibration.

For a quick visual check of the resulting calibration, stay in FreqCal mode with the Measure option cleared. WSJT-X shows the adjusted results directly on the waterfall and the displayed records.

WSJT-X provides a tool that can be used to determine the detailed shape of your receiver’s passband. Disconnect your antenna or tune to a quiet frequency with no signals. With WSJT-X running in one of the slow modes, select Measure reference spectrum from the Tools menu. Wait for about a minute and then click Stop. A file named refspec.dat appears in your log directory. When you check Ref Spec on the Wide Graph, the recorded reference spectrum will then be used to flatten your overall effective passband.

Measure phase response under the Tools menu is for advanced MSK144 users. Phase equalization is used to compensate for group-delay variation across your receiver passband. Careful application of this facility can reduce intersymbol interference, resulting in improved decoding sensitivity. If you use a software-defined receiver with linear-phase filters there is no need to apply phase equalization.

After a frame of received data has been decoded, Measure phase response generates an undistorted audio waveform equal to the one generated by the transmitting station. Its Fourier transform is then used as a frequency-dependent phase reference to compare with the phase of the received frame’s Fourier coefficients. Phase differences between the reference spectrum and received spectrum include contributions from the originating station’s transmit filter, the propagation channel, and filters in the receiver. If the received frame originates from a station known to transmit signals having little phase distortion (such as a station known to use a properly adjusted software-defined transceiver), and if the received signal is relatively free from multipath distortion so that the channel phase is close to linear, the measured phase differences will be representative of the local receiver’s phase response.

Complete the following steps to generate a phase equalization curve:

The three numbers printed at the end of each MSK144 decode line can be used to assess the improvement provided by equalization. These numbers are: N = Number of frames averaged, H = Number of hard bit errors corrected, and E = Size of MSK eye diagram opening.

Here is a decode of K0TPP obtained while Measure phase response was measuring the phase response:

The "^" symbol indicates that a phase measurement is being accumulated but is not yet finished. The three numbers at the end of the line indicate that one frame was used to obtain the decode, there were no hard bit errors, and the eye-opening was 1.2 on a -2 to +2 scale. Here’s how the same decode looks after phase equalization:

In this case, equalization has increased the eye-opening from 1.2 to 1.6. Larger positive eye openings are associated with reduced likelihood of bit errors and higher likelihood that a frame will be successfully decoded. In this case, the larger eye-opening tells us that phase equalization was successful, but it is important to note that this test does not by itself tell us whether the applied phase equalization curve is going to improve decoding of signals other than those from the reference station, K0TPP.

It’s a good idea to carry out before and after comparisons using a large number of saved wav files with signals from many different stations, to help decide whether your equalization curve improves decoding for most signals. When doing such comparisons, keep in mind that equalization may cause WSJT-X to successfully decode a frame that was not decoded before equalization was applied. For this reason, be sure that the time "T" of the two decodes are the same before comparing their end-of-line quality numbers.

When comparing before and after decodes having the same "T", keep in mind that a smaller first number means that decoding has improved, even if the second and third numbers appear to be "worse". For example, suppose that the end-of-line quality numbers before equalization are 2 0 0.2 and after equalization 1 5 -0.5. These numbers show improved decoding because the decode was obtained using only a single frame after equalization whereas a 2-frame average was needed before equalization. This implies that shorter and/or weaker pings could be decodable.

All QSO modes use structured messages that compress user-readable information into fixed-length packets. JT4, JT9, and JT65 use 72-bit payloads. Standard messages consist of two 28-bit fields normally used for callsigns and a 15-bit field for a grid locator, report, acknowledgment, or 73. An additional bit flags a message containing arbitrary free text, up to 13 characters. Special cases allow other information such as add-on callsign prefixes (e.g., ZA/K1ABC) or suffixes (e.g., K1ABC/P) to be encoded. The basic aim is to compress the most common messages used for minimally valid QSOs into a fixed 72-bit length.

Information payloads for FST4, FT4, FT8, Q65, and MSK144 contain 77 bits. The 5 additional bits are used to flag special message types used for nonstandard callsigns, contest exchanges, FT8 DXpedition Mode, and a few other possibilities. Full details have been published in QEX, see The FT4 and FT8 Communication Protocols.

A standard amateur callsign consists of a one- or two-character prefix, at least one of which must be a letter, followed by a digit and a suffix of one to three letters. Within these rules, the number of possible callsigns is equal to 37×36×10×27×27×27, or somewhat over 262 million. (The numbers 27 and 37 arise because in the first and last three positions a character may be absent, or a letter, or perhaps a digit.) Since 2²⁸ is more than 268 million, 28 bits are enough to encode any standard callsign uniquely. Similarly, the number of 4-digit Maidenhead grid locators on earth is 180×180 = 32,400, which is less than 2¹⁵ = 32,768; so a grid locator requires 15 bits.

Some 6 million of the possible 28-bit values are not needed for callsigns. A few of these slots are assigned to special message components such as CQ, DE, and QRZ. CQ may be followed by three digits to indicate a desired callback frequency. (If K1ABC transmits on a standard calling frequency such as 50.280, and sends CQ 290 K1ABC FN42, it means that s/he will listen on 50.290 and respond there to any replies.) A numerical signal report of the form –nn or R–nn can be sent in place of a grid locator. (As originally defined, numerical signal reports nn were required to fall between -01 and -30 dB. Recent program versions 2.3 and later accommodate reports between -50 and +49 dB.) A country prefix or portable suffix may be attached to one of the callsigns. When this feature is used, the additional information is sent in place of the grid locator or by encoding additional information into some of the 6 million available slots mentioned above.

As a convenience for sending directed CQ messages, the 72-bit compression algorithm supports messages starting with CQ AA through CQ ZZ. These message fragments are encoded internally as if they were the callsigns E9AA through E9ZZ. Upon reception they are converted back to the form CQ AA through CQ ZZ, for display to the user.

To be useful on channels with low signal-to-noise ratio, this kind of lossless message compression requires use of a strong forward error correcting (FEC) code. Different codes are used for each mode. Accurate synchronization of time and frequency is required between transmitting and receiving stations. As an aid to the decoders, each protocol includes a “sync vector” of known symbols interspersed with the information-carrying symbols. Generated waveforms for all of the WSJT-X modes have continuous phase and constant envelope.

The best source of help in setting up your station or configuring WSJT-X is the WSJTX Group at email address wsjtx@groups.io. The chances are good that someone with similar interests and equipment has already solved your problem and will be happy to help. To post messages here you will need to join the group.

One of your responsibilities as a WSJT-X user is to help the volunteer programmers to make the program better. Bugs may be reported to the WSJTX forum on Groups.io Post Message or the WSJT Developers list (wsjt-devel@lists.sourceforge.net). Again, you will need to join the group or subscribe to the list.

To be useful, bug reports should include at least the following information:

Suggestions from users often result in new program features. Good ideas are always welcome: if there’s a feature you would like to see in WSJT-X, spell it out in as much detail as seems useful and send it to us at one of the email addresses given a few lines above. Be sure to explain why you think the feature is desirable, and what sort of other users might find it so.