When testing the electability of a signal, remember that no object is
   anonymous in EM.  What you are hiding is your message, not your radio.
   So you would get a radio with high enough sample rate and sensitivity
   to profile the emissions of your transmitter to your specific
   transmitter, and see if your burst profiles could be reconstructed to
   recover the encrypted streams.
   Only somebody like a military specialist would ever be able to
   compromise a signal that way, of course.