The only software we know of, that could convert or at least work with both .sm3 and .sm2 files, would be XPMPro spectrum analyzer. Probably used or attempted to resave version 3 to version 2 of the same format.
Convert RHK Technology proprietary file format to RHK Technology proprietary file format.
We found one software available in the database for this conversion.
Microsoft Windows software - convert sm3 to sm2 on Windows
A spectrum analyzer for Windows.
Convert from sm3 file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.