I have an SW-3B in regular use with a Sotabeams linked dipole fed with 10m RG174 from time to time (although usually an EFHW but that’s not specific to your question) so pretty much the same setup
Mine is the slightly older model so the bar graph does not give an indication of TX power (as per the original version design) but the red led does indeed light up and TX flash in the display.
Perhaps it’s some peculiarity of the new model and the meter display mod is not quite right
Dec
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