i'm tentatively moving forward on the rtlsdr approach.
   I've found an rtlsdrblogv3 dongle, a pigtail adapter I can cut to wire
   to a probe, and i've instally pysoapysdr on a system.
   i'm thinking it could be a few phases. first, measure a signal at all,
   using direct sampling.
   then, store the signal to a disk. thinking on a quick format. maybe a
   dedicated directory containing paired files: a binary vector of
   complex64s (with real component 0 for real-valued data), each with
   adjacent json metadata.
   I was going to do sqlite but this system doesn't have py3 sqlite at
   this time, and it's about as complex to relearn the api as to set up
   the dirtree, maybe a little more.
   but first, measure a signal at all, using direct sampling.
   it gets harder for me near the radio being powered.