Yes, that was the mystery in the first place. The microphone that comes with the radio is a speaker mic and so there is audio going to the speaker in it.? It takes the audio from the earphone plug, bypassing that!? So anything you can hear from that plug is so tiny that it's not worth listening to. And the audio in the speaker-mic is so low as well, it's useless in any kind of noisy space.
Why this is not explained in the manual or elsewhere, I don't know. I even? opened up the radio twice? trying to find out what was wrong, but accidentally left the mic off once, and bang! Full audio from the earphone plug, suitable for amplification into a full room-sound quality result!
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Bob, KL7EAL Los Angeles
Robert G. Aldrich