I added a different antenna. I got an old Radioshack antenna which has an enclosed UHF loop and rabbit ears. More FM stations and more RDS data.
Gqrx has really helped a lot because knowing so little I feel blind otherwise. It gives me a good starting point to move on to the next phase of my learning. Thanks to all those many contributors to Gqrx (and there are many).
I have Gnuradio working with all the moving parts and now I will try to see if I can get ADS-B working. FWIW ADS-B is broadcast from aircraft constantly at 1Hz over 1090Mhz. So I need to set up a flowgraph and see what happens. I think first I will try to capture raw data, either in Gqrx or Gnuradio.
I made an antenna like this one: