WSJT-X User Guide

WSJT-X 3.0 incorporates all developments successfully tested up to WSJT-X Improved 2.8.0 and a number of new items. The list below summarizes important new features. For more details you should carefully read the sections in this guide linked in the following notes, especially if you have not previously used WSJT-X Improved.

This guide includes many screen shots to illustrate user settings and program features. Keep in mind that WSJT-X is a multi-platform application; the detailed appearance of windows and user controls will be 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.

Most people access the WSJT-X User Guide primarily through a browser. Use the browser’s search function, generally invoked from the keyboard with the keys CTRL+F, to search the guide for help on a particular topic or keyword.

The names of WSJT-X windows, menus, and on-screen controls are displayed in this manual in boldface type, as in Wide Graph. File names and information entered via keyboard is shown in a monospace font, for example all.txt.

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 or Japanese, start a command-prompt window and enter one of these the commands:

wsjtx --language es

wsjtx --language ja

The top portion of the main window will then look like one of the following examples:

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. Bug reports and suggestions for new features, improvements to the WSJT-X User Guide, etc., may be sent to one of the email lists listed in the Support section. You must join the group in order to post messages to the email list.

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

Download and execute the package file wsjtx-3.0.0-rc1-win32.exe (Windows 7 or later, 32-bit) or wsjtx-3.0.0-rc1-win64.exe (Windows 7 or later, 64-bit) following these instructions:

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

You can download a suitable OpenSSL package for Windows from Windows OpenSSL Packages; you need the latest Windows Light version. For the 32-bit WSJT-X build, use the latest Win32 v1.1.1 version of the OpenSSL libraries, for the 64-bit WSJT-X use the latest Win64 v1.1.1 version of the OpenSSL libraries (Note: it is OK to install both versions on a 64-bit system) which, at the time of writing, were Win32 OpenSSL Light Package and Win64 OpenSSL Light Package respectively.

Install the package and accept the default options, including the option to copy the OpenSSL DLLs to the Windows system directory. There is no obligation to donate to the OpenSSL project. Un-check all the donation options if desired.

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:

For macOS10.13 and later, download the file wsjtx-3.0.0-rc1-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:

This menu appears on the Macintosh only. Settings appears here, labeled as Preferences, rather than on the File menu. About WSJT-X appears here rather than on the Help menu.

Some users prefer to create and use entries on the Configurations menu for switching between modes. Simply Clone the Default entry, Rename it as desired, and then make all desired settings for that configuration. All settings will be restored whenever you select that configuration.

As well as switching between configurations while running WSJT-X, you can also start the application from the command line in any desired configuration. Use the command-line option --config <configuration-name>, or -c for short, as in these examples for configurations named FT8 and Echo:

Most items on the View menu can be clicked to display a specified window. Some are self-explanatory or described in detail elsewhere in this guide; additional details for others are included below.

Active Stations is a window with two distinct purposes. The first can help you work the most distant stations, in particular for the distance-scored ARRL International Digital Contest. You can set the maximum length of the list and the maximum “Age” of displayed decodes, measured in Rx sequences. You can request display of only ready-to-be-called stations: those whose most recent transmission is a CQ, RR73, or 73 message. For the ARRL International Digital Contest the window displays scoring Rate (points in the most recent hour), your total accumulated Score, and the number of Band Changes in the past hour.

When WSJT-X is used together with sister program QMAP, the Active Stations window displays the frequencies, SNRs, Q65 sub-modes, and Maidenhead locators for stations recently decoded by QMAP over its full 90 kHz bandwidth. Stations using a 30-second sub-mode of Q65 are highlighted in yellow. You can limit the displayed list by checking the Wanted only and/or CQ only boxes. The total number of QSOs found in wsjtx.log is shown, for example to follow your progress in an EME contest.

SWL Mode reduces the main window to show just the menus, decodes windows, and status bar. You may find this useful when running multiple instances of the application. The size and location of the main window are saved and recalled independently for this view.

A special messaging system can be used to invite your QSO partner to move to another band or mode (for example, during a contest), or to convey some short canned messages. There are two main parts, the Message Creator and the QSY Monitor. Received messages are displayed in popup windows.

Use the Message Creator to create and send these special messages with just a few clicks. When using this feature for the first time, make sure that your IARU Region has been set (upper right on the File | Settings | General tab). Activate the Message Creator window by checking its name on the View menu. Four tabs are available: HF, VHF, EME and General:

To send a message, select the appropriate tab and then the band, mode, and kHz part of frequency for a QSY request, or a canned message from the General tab. The actual message to be sent will be shown in the field labeled Message on each tab. Click Send Message to have this message conveyed in your next scheduled transmission. Enable Tx will be activated automatically, and your message will be sent to the callsign in the DX Call field of the main window. The example below shows the creation of a message to W3SZ asking him to QSY to 145.550 using FM.

To prepare for receiving special messages, check Enable Message Popups on the View menu. A screenshot showing the example message sent to W3SZ is shown below. As recipient, W3SZ can click Reply Yes or Reply No, and his reply message will be sent in the next Tx interval to the callsign present in the recipient’s DX callsign box.

You can view messages sent to other stations, as well as to yourself. To do so, check QSY Monitor on the View menu. An example showing a number of received messages is shown below.

Optional band select buttons can be switched on or off from the View menu. Two sets of buttons are available. Check Band Buttons to get an HF-oriented set for 160 m through 70 cm, and also VHF / UHF Buttons to display a set for 8 m through 24 GHz. Clicking on a band button switches the program to a mode-dependent default frequency selected from the frequency table for that band. In FT8 mode, right-clicking a band button will set dial frequency to the conventional DXpedition frequency (or on 6 m, to the intercontinental frequency). To define your own preferred default frequencies, check the relevant Pref boxes on the File | Settings | Frequencies tab.

Select Dark Style to switch to a dark-background theme for all windows. To make it effective you will probably want to redefine your color settings.

The Filters menu lets you control a wide variety of message-filtering options. Many of them are defined on the File | Settings | Filters tab. You can hide, ignore, or highlight stations worked before on the current band, worked today or yesterday, or those present in the Ignore List. A checkbox labelled BP on the main window (just left of the Log QSO button) allows all filtering options to be bypassed temporarily with a single click. This action can be used, for example, if you have filtered out your own continent to display only DX stations but now wish to monitor all band activity.

All WSJT-X modes offer Fast, Normal, and Deep decoding options. Deep usually provides the best sensitivity, but at the cost of slower processing and a slightly higher probability of false decodes. In FT8 mode you can select a multithreaded decoder with additional options that are tunable for best overall performance in your setup.

Full Duplex Mode can also be selected from the Decode menu. Audio input can be taken from a second local receiver or from a WebSDR on the internet. Duplex operation works for slow modes (FT8, FT4, Q65, … ) and fast modes like MSK144. Your own transmitted messages will be highlighted in the Band Activity window in the color you selected for "Transmitted message" on the File | Settings | Colors tab.

An additional option to disable mouse clicks on the waterfall, visible only when Q65 mode is selected, and VHF Features are enabled, can be selected to prevent inadvertent mouse clicks on the waterfall from changing the Rx and/or Tx offset frequencies. When selected, frequency changes can still be made using the mouse by holding down the ALT key.

You can control the types of information that _WSJT-X saves during an operating session, perhaps for future analysis or diagnostic purposes. For example, check Save decoded to save audio files for all receiving sequences producing at least one decode. The file ALL.TXT is a record of everything you have transmitted or received. You can choose to have it automatically split into smaller chunks by month or year, or to disable it entirely. Some diagnostic logging of events always takes place. Diagnostic mode lets you collect more data to troubleshoot problems with the program, or with its communication with your rig.

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.) Meanings of remaining options on the General tab should be mostly self-explanatory after you have made some QSOs using WSJT-X. You can 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 example shown below.

Companion programs like JTAlert use the UDP Server feature to exchange information with WSJT-X. If you are using JTAlert to send requests to WSJT-X, be sure to check the box Accept UDP requests.

By default, the Working Frequencies table contains a list of frequencies conventionally used for specific modes. 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.

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.

Some users find an alternative color scheme with pastel-like colors easier on the eyes and more suitable for the dark style. You can select either the original WSJT-X or the alternative style. With the alternative style, stations uploading their logbook to LoTW will have black foreground color, others red. Stations worked-before are displayed with grey background.

It is still possible for you to customize the color scheme according to your own preferences. In addition, you can highlight individual callsigns or grids according to your specifications. Callsigns and/or grids can be highlighted with orange or blue background color. Callsigns/grids must be separated by commas and can be mixed (e.g. "K1JT, DG2YCB, JO33, JN58,"). You must include a comma after each callsign or grid, and also at the end of the line.

Special Operating Activity

WSJT-X can be configured to issue audible alerts when messages with specified content are decoded. This feature requires computer access to at least two audio output devices: one for transmitted audio, and a different one for audible alerts. The device for transmitted audio is selected on the Audio tab; alerts are always played on the Default audio device, most commonly the loudspeaker of your computer. To activate audio alerts, check any desired boxes on the Alerts menu and click the button Enable Audio Alerts.

Categories above the line require checking the box Show DXCC, grid and worked before status in the Display section of the File | Settings | General tab. To identify what triggered one of these alerts, ensure that corresponding categories in the File | Settings | Colors tab are selected. Use the checkboxes Highlight DX Call in message and Highlight DX Grid in message in the Display section of File | Settings | General to help identify what triggered an alert for DX Call or DX Grid in message.

Filters provide a way to limit what is displayed in the Band Activity window. Define desired filtering categories using entry fields and checkboxes on the Filters tab. You can turn many filters on or off by checking lines on the main-window Filters menu.

You can specify up to four territories for which hiding messages can be switched on or off using options on the main window Filters menu. You can hide messages from a specific continent, or stations worked before on a band. There are entry fields for a Blacklist, a Whitelist, and an Always Pass list, and these can be used in combination. Blacklist might be used to suppress decodes from pirate stations, contest messages, or other messages with unwanted content. You can enter whole callsigns, parts of callsigns, or keywords. Whitelist can be used if you’re interested only in messages with certain grids, calls, or keywords. All other messages (except those allowed by the Always Pass list) will then be suppressed. Always Pass will enable display of decodes from specific stations even though the respective country or continent is hidden.

You can optionally apply filters only to callsigns of transmitting stations, or use the filters only for Wait and Pounce operation. In the latter case, all messages will be displayed in the Band Activity window, but Wait and Pounce will respond only to stations that meet the set filter criteria.

When any filter is active that limits display of some decodes, the status label at bottom left of the main window changes from green "Receiving" to cyan "Receiving, Filters on".

A click on the Ignore button (located on the main window below the DX Grid box) adds the callsign present in the DX Call box to your Ignore List. If you have also checked the box Ignore stations from the Ignore List on the main-window Filters menu, such stations are automatically ignored when you use one of the CQ: …​ options or Wait and Reply. The "Ignore List" will be created in your log directory the first time a station is added to it. You can erase the "Ignore List" from the File menu.

Select Keyboard shortcuts from the Help menu (or use function key F3) to display the following list of quick-action shortcuts:

Select Special Mouse Commands from the Help menu (or use function key F5) to display the following list of mouse commands:

The following steps will download sample audio Wave files that were originally recorded by WSJT-X. These files can be opened and processed at another time, to partially simulate real-time operation.

The WSJT-X Wide Graph window displays the frequency spectrum of received audio. Usually, the upper portion 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 Spec nn% at the bottom right lets you adjust 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 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 main window will illuminate three times, once for each pass. The first decoding attempt in each 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 now has two additional 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:

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".

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 sequences provide better sensitivity only if Tx and Rx frequency instability and channel Doppler spread are small enough that received signals will 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. (See Table 7 in the Protocol Specifications section.) For example, the keying rate for FST4-1800 is 0.089 Baud, so successful operation requires frequency stability to be better than (and Doppler Spread less than) around 0.05 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 control is located just above the input level thermometer.) The NB 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. A 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 essentially invisible on the Wide Graph 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 or SNR) 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 his next transmission, 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 sometimes add 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 WSJT-X 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 hardly enough time, so 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, or the strongest or weakest responder.

Three wait-to-transmit features are available: Wait and Reply, Wait and Call and Wait and Pounce. Enable these features through a checkbox near the bottom of the File | Settings | General menu. When they are enabled, the DX Call field and Enable Tx button turn yellow to warn you that an automatic transmission may occur when a specified condition is met. Be alert, and take any necessary precautions!

If a callsign is present in the DX Call field, Wait and Reply will attempt to continue your QSO when that station sends you a message. For example, you may have called station K1ABC, received no reply and stopped transmitting when K1ABC replied to someone else. If K1ABC then calls you, your QSO will resume automatically. This feature also ensures that you will send a second RR73 if your first one is not answered. Wait and Reply is effective for all modes where auto-sequencing is available and a callsign is present in the DX Call field.

Wait and Call is useful if the station you wish to work disappears for a time, perhaps in a deep fade. To enable the feature, click on the DX Call label, which will turn red if a callsign is present in the DX Call field. When the station is decoded again sending a message containing CQ, RR73, RRR or 73, you will call him automatically up to three times. Any manual intervention, such as pressing the Halt Tx or Stop buttons, will disable Wait and Call and give you the normal manual control over the QSO.

Wait and Pounce can be used to answer a CQ from another station with specific selection criteria. To activate Wait and Pounce, ensure that the DX Call box is empty and select one of the applicable CQ categories from the drop-down list on main window. Then right-click on the Enable Tx button, which will turn orange. In your next Tx sequence a reply will be sent automatically to a CQing station that satisfies your chosen selection rule.

Wait and Pounce works in concert with the Filters feature. For example, you can wait for CQ messages containing a certain prefix, grid, callsign, or keyword.

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, WW Digi, and ARRL International Digital 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 File | 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:

Compound or nonstandard callsigns are automatically recognized and handled using special message types. 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 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 base call and 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-X modes, be sure to go through the Basic Operating Tutorial above as well as the following checklist:

To activate the VHF-and-up features:

Successful setting of split operation can be verified by checking that S is embedded in the indicator between the band combo box and the dial frequency indicator. In some circumstances the S may only appear after a frequency or band change. If the S is not present, Doppler correction will not function.

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, Enable AP, and Auto Clear Avg after decode.

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: EME, tropospheric scatter, rain scatter, ionospheric scatter, trans-equatorial propagation (TEP), and the like. The following screen shot shows the Wide Graph and decoded text windows after processing a Q65-60A sequence received via EME on 6 meters, by W7GJ Transmissions are decoded from N0TB, N8JX, W1VD, and VE1JF, all by the EME path.

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.

Here’s a similar screen shot for a 6 m ionospheric scatter signal over the 1155 km path from K9AN to K1JT, using submode Q65-30A. The received signal was barely audible most of the time.

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, even on bands as high as 432 MHz. 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:

The use of this feature is recommended when the calling channel is busy, as it allows QSOs to be conducted on a frequency of your choice free of QRM. For example, if you wish to call CQ on 144.360MHz and conduct your QSO on 144.388MHz, follow the steps below:

Your CQ message in Tx6 containing your offset frequency will then be transmitted at 144.360, and your radio will be set to 144.388MHz on receive when your CQ call completes. Subsequent QSO messages will be transmitted on 144.388MHz.

On reception, when you double-click on a message like CQ nnn K1ABC FN42 your rig will QSY to the specified QSO frequency. Thr QSO will then take place on that frequency.

Echo mode provides tools for two types of measurements: lunar echoes of your own transmitted signal, and broadband noise power received from the Sun, Moon, and other sources including ambient-temperature ground and nearby objects. Such measurements are widely used for optimizing a station’s capabilities for Earth-Moon-Earth (EME) communication. In addition, you can generate lunar echoes of short alphanumeric messages for demonstration and amusement purposes.

For quantitative measurements the Echo-mode transmission is a fixed-frequency 1500 Hz tone lasting 2.048 s. After sending it WSJT-X switches back to receive, records the lunar echo about 2.5 s later, computes its spectrum, and displays results. The program takes care of necessary T/R switching and frequency adjustments for Doppler compensation. To make such measurements, be sure to check Enable VHF and submode features on the File | Settings | General tab. Set Split Operation to Rig or Fake It on the Settings | Radio tab, Doppler tracking and Own Echo or Constant frequency on Moon on the Astronomical Data window.

Select Fixed Tone on the main window, point your antenna at the Moon, and click Enable Tx to start a sequence of measurements. Each Echo-mode cycle takes 6 seconds. The average echo spectrum will be displayed in the Echo Graph window, and measurements appear in the main window. If echoes are strong enough they will be visible in the waterfall, centered at 1500 Hz. A spinner control labeled Avg (to the left of the Decode button) controls averaging of successive Echo sequences. Displayed SNR and the plotted Echo spectrum will be averaged over the selected number of sequences.

Each echo cycle produces a line of data in the main window with the following information:

In addition to the traditional Echo mode, for amusement you can transmit short messages (up to six alphanumeric characters) and receive their echoes, using either multi-tone frequency-shift keying or standard Morse code. For the former, select MFSK, set a suitable tone spacing at least one-third of the expected Doppler spread, and enter your callsign in the field provided. If your radio’s dial frequency is controlled in 10 Hz steps, use tone spacing of at least 20 Hz.

After you click Enable Tx, WSJT-X will send a sequence of six tones, each lasting 0.341 s, to convey the characters in the entry field. Message encoding is trivial, with no forward error correction: each tone has a frequency offset from 1500 Hz corresponding to the position of that character in the sequence 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ. Lines displayed in the main text window will then include three additional items:

Note that when MFSK is selected and Avg is set to anything larger than 1, the decoded echo message will be averaged indefinitely, until you click Clear Avg.

Here’s an example of MFSK echo testing at 10 GHz, from DL3WDG. You can easily see the five distinct callsign characters 3 D G L W (in order of increasing tone frequency) in the waterfall. The spectrum plotted in the Echo Graph window is the average of all six tones, with their individual frequency offsets removed. The full width of the echo signal near the baseline is very close to the predicted value, 66 Hz.

Select CW to send a short message by Morse code, repeated with the usual 6 s Echo cycle. If you can hear your own echoes, this feature is especially good for demonstration purposes. Code speed will be automatically adjusted so the message just fits into the allotted 2.048 s Tx interval. The most useful CW messages will be short and simple, such as “O” or “OO”.

System timing details are important. Echo-mode features work best when the station’s T/R switch-over times are no longer than a few hundred milliseconds in each direction. In most amateur EME setups these times are determined by programmed software delays, response time of a CAT-controlled transceiver, and any hardware sequencers in use.

Most Echo-mode features require Doppler compensation via CAT control of your radio. You may find it important to experiment with software options that affect system timing. Use the radio’s Monitor function (or listen on another receiver) to make sure that in MFSK mode you transmit all six tones at their full programmed length. Try sending message sequence “07ELSZ”, for example. Tx delay (set on the File | Settings | Advanced tab) should be no larger than necessary. Experiment with setting Split Operation to both Rig and Fake It on the File | Settings | Radio tab. Doppler tracking by Own Echo might work better than Constant Frequency on Moon.

Measurements of noise from the Sun, Moon, and ground are made relative to that from a suitable "cold sky" direction. For example, you may want to make potential improvements to your system that will maximize the difference between Level when pointed at the Sun, and when pointed away by several beamwidths or more. Click Monitor to start a continuous sequence of noise measurements.

Until the advent of Q65, digital EME has mostly been done with 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 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 2.3 GHz, Q65-60D on 3.4 and 5.7 GHz, Q65-60D or E on 10 GHz, and Q65-60E on 24 GHz and higher bands.

JT4, JT65, and Q65 offer message averaging — the summation of successive transmissions conveying the same message — to enable decodes at signal-to-noise ratios several dB below the threshold for a single transmission. 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. These options can be activated from the Decode menu.

With a CAT-controlled radio, WSJT-X can be used to compensate for changing Doppler shifts during a CW EME QSO. This capability is especially useful on the higher microwave bands, where Doppler shifts are large. Put your rig in CW mode and set the option File | Settings | Radio | Mode | None to prevent WSJT-X from trying to change the operating mode. Use the Tune button to switch between receiving and transmitting. No tones will be transmitted as the rig is in CW mode; but importantly WSJT-X knows you are transmitting and adjusts the dial frequency as needed for the currently selected Doppler tracking mode. Click Tune again to revert to receive mode, reactivating the proper Doppler corrections for receiving.

WSJT-X supports the use of large additional offsets in dial frequency for transmitting and receiving — for example, to allow EME QSOs between countries with amateur frequency allocations at 2304 and 2320 MHz. To use the feature, first set the Sked frequency to the frequency you want to use for receiving in the normal way. Next, select the amount you want your transmitted frequency to be shifted. The figure below shows an example of a station receiving on 1296 MHz and transmitting on 1298 MHz. In this case, a Tx shift of +2 MHz has been selected.

The following controls appear just under the decoded text windows on the main screen. The top row appears only if Band Buttons is checked on the View menu, and some controls on the second row are visible only when a relevant mode is in use.

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, JT65, Echo, and for toggling FT8 Hound mode ON or OFF. If Enable Wait features is checked on the File | Settings | General tab and a callsign is present in the DX Call box, the DX Call button turns yellow to warn that your station is primed to transmit.

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 disabled or removed from the display.

Controls used for messages to be transmitted appear on Tab 1, which provides 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 a received message 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.

If Show distance/azimuth with grid is checked, decoded messages including the transmitting station’s locator will be displayed with the calculated distance and great-circle azimuth from your location.

Check Align DXCC / distance / azimuth to keep DXCC names or principal prefixes as well as distance and azimuth in an aligned table form. Two spin boxes allow further configuration of your preferred layout: the first sets the number of spaces between the decoded message and the DXCC name; the second sets the number of spaces between the DXCC and the distance/azimuth field.

The following screen shot shows an example Band Activity pane with Show distance in messages with grid, Show azimuth in messages with grid and Align DXCC / distance / azimuth enabled.

US States can be optionally appended to the decoded messages. Check Map Grid locator to U.S. State to do this for CQ calls only, or Show U.S. States in messages with grid to include all messages containing a grid locator. Where a grid locator’s region overlaps more than one State, all possibilities are presented.

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. Tune to a quiet frequency with no signals or birdies. With WSJT-X running in one of the slow modes and Monitor active, make sure that Flatten is checked on the Wide Graph and then select Measure reference spectrum from the Tools menu. Wait for about a minute and then click Stop. A file named refspec.dat will appear 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 inter-symbol 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 will be one of these email lists: wsjt-devel, WSJTX Group, WSJT Group, or wsjt-x-improved-community. 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 in any of these forums 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 one of the email lists mentioned above. Again, you will need to 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.