How do I log only received information in RealTerm
I just downloaded RealTerm and did some testing:


"Half Duplex" (strangely enough) appears to be the equivalent of "local echo", however that only works to turn off outgoing data for screen display (although see the last item below).
The diagnostic log file seems to capture incoming and outgoing data regardless. If you need to use this method you might look at "Diagnostic Files: Trace and Log", but I don't know if that will help. 
With "Direct Capture" enabled, the "Capture" option appears to only capture incoming data and you can include a time stamp if the data from your sensor is terminated with a carriage-return and line-feed. It does not seem to include all the diagnostic data of the log file.
If you only need to capture incoming data, use the "Capture" option and turn off "Direct Capture". This will capture everything that goes to the screen display; therefore to only capture incoming data, un-check "Half Duplex" on the "Display" tab.