From: grarpamp <grarpamp@gmail.com>
   Subject: Stealing Keys from PCs using a Radio
   Even  in 1977, when I had just built my 'Dyna Micro'
   [1]https://en.wikipedia.org/wiki/Single-board_computer  microprocessor
   trainer board, I could tell that its emanations on the AM radio band
   were were quite distinctive:  I could monitor the progress of programs
   merely by listening to an otherwise-unoccupied AM frequency.  While I
   wasn't particularly interested in the details at that time,  it has
   long been obvious that a program could be written to emit specific
   data, perhaps by repeating segments of code based on the information to
   be transmitted.
                  Jim Bell

References

   1. https://en.wikipedia.org/wiki/Single-board_computer