Hi - the OP is back and ready to conclude that my problem was a defective radio.
I did the radio tests suggested, with limited success. RSSI improved slightly upon changing the filters, but still couldn’t hear the same stations my R30 picks up clearly.
Logical next step, try another SDS100....so I got my hands on one, and in the same backyard spot it’s wiping the floor with my original radio. Just inside at my kitchen table it’s still picking up signals 10-20 miles away in NJ and CT. Still not nearly as good as the R30 on airband, and I don’t live in the world’s best listening area, but I’m starting to feel a lot less crazy. Sending the SDS100 back for repair and looking forward to seeing what it can do.
Thanks for everyone who volunteered suggestions. I really appreciate the help eliminating all the possibilities.