JTDX installation notes (starting from v17.0)

JTDX.INI file is responsible for configuration settings storage, to get to the folder with this file in JTDX software open File → Open log directory

Folder with JTDX.INI file is created upon first run of software and will remain if software is uninstalled.

Data structure in this file can may be different for various JTDX versions. JTDX.INI file compatibility with previous software version is shown in the release notes.

Upon JTDX software upgrade it is recommended to delete old JTDX.INI file, according to information from the release notes, all settings will reset to default values if this file is deleted.

This file may only be deleted if software is closed, otherway JTDX software will recover old JTDX.INI file from the backup copy.

If user would like to use various JTDX versions or multiple instances of the same JTDX software version simultaneously, shortcuts shall be used with ‘--rig-name=’ key defined in the shortcut properties to run the software. This way every instance of the running software will be using own configuration settings and log, located in the folder defined by the --rig-name= key.

HF CALL3.TXT file coming together with JTDX software, it contains callsign and grid data and being used for hinted decoders and detection of the false decodes user has to copy CALL3.TXT file in the log directory to get hinted decoders working.

wsjtx_log.adi file is used for QSO logging, ADIF export from other logbook software can be used for JTDX if it is copied in the wsjtx_log.adi file.

Old wsjtx_log.adi and CALL3.TXT files shall be copied to the new log directory if upgrade from older JTDX software version to JTDX v17.x is performed.

Sound card configuration

JTDX software works with 48 kHz sampling rate and 16 bit depth audio stream. To avoid re-sampling and decoding performance degradation it is recommended to configure input and output (recording and playback) of audio device in the operating system using this settings.

To configure it in MS Windows 7/8/10 open audio devices

Choose audio device you would like to use for JTDX and go to Properties -> Advanced tab

The same settings shall be applied for virtual audio cable, if it is used for SDR transceiver or Web SDR receiver connection to JTDX.

If there is only single sound card installed, MS Windows operating system will configure it as default audio device and some other application like Web browser or Skype may change sampling frequency of the sound card leading to the JTDX decoding performance degradation.

Time synchronization

It is important to keep computer synchronized -0.2…+0.5 second to the network, if every operator keeping similar time accuracy the maximum decoding performance can be achieved by JTDX software.

NTP client software shall be used for time synchronization, 5 hour time update interval would be good enough for most computers. Increased time update interval shall be used for unstable or low speed Internet connection.

Make sure there is only single NTP client software installed and running on your computer. There will be unstable time synchronization if multiple NTP clients are running simultaneously on the computer.

Make sure Windows automatic time synchronization is turned off.

Antivirus protection software and poor quality Internet connection may cause delays in the Internet packet propagation and in result of this delay wrong time synchronization. Make sure that Internet packet analyzis is turned off in the antivirus software

Various NTP client software is available in Internet, there is just an example of settings for the NetTime Version 3.20 Alpha 1 software.

If time offset after automatic time update is greater than 100 ms manual time update by ‘Update now’ button can be used to bring time offset below the 100 ms value.

GPS/GLONASS/Galileo receivers also may be used for time synchronization, there is an example of such usage with the SatTime 1.2 software.

Software controls. Reception

Signal decoding bandwidth

JTDX software may decode JT65 signals with synchronization pattern (bottom frequency of the signal) located in 0 to 2700 Hz AF frequency range.

Decoding bandwidth can be controlled by user and defined by horizontal size of the ‘Wide Graph’ window, ‘Bins/Pixel’ and ‘Start’ frequency settings.

For located above picture JT65 signals with synchronization patterns located between 200 and 700 Hz will only be decoded.

With the same size of ‘Wide Graph’ window, for picture located below, JT65 signals will be decoded starting from 0 and up to 2700 Hz frequency range.

Number of candidates for decoding depends on the bandwidth, number of decoding attempts per candidate might be increased if lesser bandwidth is used.

In JT65+JT9 operation mode bottom edge of JT9 signals decoding is defined by the blue marker and ‘JT65 freq JT9’ settings.

Transceiver frequency accuracy may be taken in account for JT9 signals decoding if blue marker is set 100 Hz below the recommended JT9 band bottom edge. This setting may also be adjusted during RX interval to decode JT9 signal located below the blue marker.

Filter button

Filter button limits JT65 signals decoding down to 400 Hz bandwidth and decoded messages output to the screen down to 100 Hz bandwidth. Filter is centered relatively to synchronization pattern (bottom frequency of JT65 green RX marker in the Wide Graph window).

400 Hz wide bandwidth is required in overcrowded band conditions to decode and subtract loud signals that have spectrum crossed with QSO frequency.

100 Hz bandwidth for letting message come to the screen allows user to focus attention close to the receive frequency of QSO.

Number of decoding attempts is redistributed to the lesser number of candidates slightly increasing probability to decode signals if ‘Filter’ button is used.

Hint button

‘Hint’ button activates four decoders, each of them is based on the matched filters.

Diagram below shows the way decoders being used in the JTDX software.

Three ‘Hint’ decoders use data from the CALL3.TXT file, fourth Hint decoder use data from ‘DX Call’ and ‘DX Grid’ windows.

First two ‘Hint’ decoders operate in wide bandwidth and focused on CQ /CQ DX messages, last two operate on QSO RX frequency and use full set of the standard messages including RO, RRR, RR73, 73: total 66 messages per each callsign from CALL3.TXT or from ‘DX Call/DX Grid’ windows.

This set of messages is encoded the same way software does it for message transmission, and each codeword is compared with the demodulated one using the correlation function.

Codeword set generation may take up to 20…50 seconds depending on the CPU frequency. This process is started once, and for last two ‘Hint’ decoders is triggered by candidate on the QSO receive frequency.

Created codeword set is allocated in the memory and any next receive interval will be decoded fast enough.

There are two thresholds used to make decision if message is decoded by ‘Hint’ properly: distance between first and second best codewords and absolute value of the correlation function.

There is the asterisk symbol ‘*’ added to the decoded ‘Hint’ messages, to let user distinguish Hint decodes from BM/FTRSD ones. This symbol is also used to ban sending decoded ‘Hint’ messages to the pskreporter server http://pskreporter.info/pskmap.html , as some of them may be false decodes.

There are unavoidable false ‘Hint’ decodes caused by high sensitivity of the ‘Hint’ decoders, all of them have really existing callsigns in the decoded message. Similar to CW/SSB weak signal reception it is up to user to make own decision if received message is the wrong one.

Number of the false ‘Hint’ decodes depends on linearity of the receive path, signal taken from SDR receiver with digital audio stream have less false decodes, number of the false decodes will be increased if there are intermodulation products in the receive path.

Decode button

Last receive interval or last played wav file will be decoded again if ‘Decode’ button is clicked.

It could be useful if user changed any combination of buttons Filter/Hint/SWL mode.

Left mouse’s button double click on the Wide Graph allows to choose required frequency/JT65 signal and activates ‘Decode’ button. Probability to decode JT65 signal on this frequency will raise up as there is better algorithm used for QSO RX frequency.

Stop button

Stops reception of the signals. Stops decoding of pack of the wav audio files.

Software controls. Transmission

Split operation

Split operation together with the CAT transceiver control is primarily used to prevent radiation of the AF signal harmonics, letting user to set AF signal level once and avoid constant control of this level if AF frequency being changed.

Split operation also allows to transmit JT65 signals in 0…500 Hz Wide Graph range and JT9 signals above 2500 Hz with no output power reduction and overload of AF path of the transmitter.

This functionality is inherited from WSJT-X, JTDX software will always be keeping transmit AF frequency within 1500…2000 Hz frequency range, TX VFO frequency is changed via CAT interface with 500 Hz step depending on the TX AF frequency on the Wide Graph.

There is simple example to gain understanding Split operation functionality:

Let’s say TX VFO is set to 7076.0 KHz.

If Wide Graph TX AF frequency is set to 900 Hz, TX VFO frequency will be changed to 7075.0 KHz and software will supply transmitter with 1900 Hz AF signal.

If Wide Graph TX AF frequency is set to 2300 Hz, TX VFO frequency will be changed to 7076.5 KHz and software will supply transmitter with 1800 Hz AF signal.

TX VFO tunig step is equal to 500 Hz, it is the same for Split operation/Rig and Split operation/Fake it mode.

Split operation/Rig uses both VFO A and VFO B of transceiver, one for reception another for transmission.

Split operation/Fake it is designed to support transceivers with single VFO, in this mode VFO frequency will be changed for every transmit to/from receive transition.

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