rtlsdrs are scary :) not finding one immediately nearby. likely one
   near where another miniusb cable might be.
   might _mostly_ get miniusb cable, maybe just a smidge of rtlsdr.
   can also diagnose without these things by finding ways to trigger later
   into signal. for example, I could use diodes to OR the signal with an
   unused pin at higher voltage, and engage the pin via software to decide
   where to trace.