If you have connected a radio interface either directly by RS232 or by an emulated USB port to your Mac you can’t access the interface for acquiring the frequency, mode, etc. with both programs at the same time. As MacLoggerDX has a great AppleScript interface you can create a small script that will be integrated as macro into fldigi by using the EXEC command.

The script will look like this:

tell application „MacLoggerDX“
lookup (system attribute „FLDIGI_LOG_CALL“)
delay (1)
set rawfrequency to (system attribute „FLDIGI_FREQUENCY“)
set mldxfrequency to rawfrequency / 1000000
setLogFrequency mldxfrequency
setLogMode (system attribute „FLDIGI_MODEM“)
log
end tell

The frequency needs to be converted to MHz because MLDX only wants this format. Now you can just click your macro and the QSO will be logged correctly.