0. Another computer or virtual machine shall be used to avoid breaking existing JTSDK2, installation to disk C:, at least 25GB disk space required, SSD is preffered as HDD runs too slow.
Download and install JTSDK3 as per instructions from this link: https://sourceforge.net/projects/jtsdk/files/win64/3.1.0/
Use option 'd' (default) for Qt installation there.
 

1. In folder C:\JTSDK64-Tools\tools\Qt run MaintenanceTool.exe
Select display 'latest releases' and in the provided list select Mingw73_64 for Qt 5.14.1 and deselect Qt 5.12.4, do not change settings for 'developer and designer tools'. Install Qt 5.14.1.

2. Download CMake v3.16.4 from :
https://github.com/Kitware/CMake/releases/download/v3.16.4/cmake-3.16.4-win64-x64.zip
Unzip it, rename cmake folder (for instance to _cmake) in C:\JTSDK64-Tools\tools and copy unzipped 4 folders into C:\JTSDK64-Tools\tools\cmake\3.16.4 folder

3. Copy in C:\JTSDK64-Tools modified files jtsdk.cmd, jtsdk-setup.cmd and jtbuild.com

4. Rename in C:\JTSDK64-Tools\config empty file qt5.12.4 to qt5.14.1

5. Copy in C:\JTSDK64-Tools\config empty files: autorun, clean, hlclean, reconfigure, separate

6. Copy in C:\JTSDK64-Tools\tools\scripts modified file setqtver.cmd

7. modified C:\JTSDK64-Tools\src\jtsdk64-tools\src\msys2\src\bin\build-hamlib.sh

find this line
    LIBUSBD="/$DRIVE/JTSDK64-Tools/tools/libusb/1.0.22/MinGW64/dll"

and add this line
    LIBUSBS="/$DRIVE/JTSDK64-Tools/tools/libusb/1.0.22/MinGW64/static"

modified case $QTV in ,from 5.13.0 to 5.14.1

modified #copy dll , add these lines

    echo "* $LIBUSBS/libusb-1.0.a"
    cp -u "$LIBUSBS/libusb-1.0.a" "$PREFIX/lib"
    echo "* $LIBUSBINC/libusb-1.0\libusb.h"
    cp -u "$LIBUSBINC/libusb-1.0\libusb.h" "$PREFIX/include"

remark : if hamlib not need #git update, use "#" to disable these lines like below:
        #    git pull
        #    git clone git://git.code.sf.net/u/bsomervi/hamlib src
        #    git checkout integration



8. modified C:\JTSDK64-Tools\tools\msys64\home\user\src\hamlib\src\hamlib.pc.in

   Libs.private: -lusb-1.0 @MATH_LIBS@ @DL_LIBS@ @NET_LIBS@ @PTHREAD_LIBS@



9. Copy in C:\JTSDK64-Tools\tools\msys64\home\[account name]\src\hamlib src folder
   with modified Hamlib source code as of 20200114 (do not use previous versions)

10. Start JTSDK64-Tools from Start->Program Files, type msys2, type menu
    and type 6 update msys2 again and again, until msys2 is nothing update.
    and then type 5 build Hamlib selection in menu.

11. Exit msys2 and qtpy(JTSDK64-Tools)
12. Start JTSDK64-Tools, and run jtbuild.cmd once
13. Copy JTDX source code (wsjtx folder) in C:\JTSDK64-Tools\tmp
14. Run from qtpy(JTSDK64-Tools) command 'jtbuild rinstall'
