[HH] Mystery signal from a helicopter

[Tom Metro]

A self-taught signals & electronics hacker from Helsinki spotted a
curious pattern in an audio recording of a helicopter and figured out
how to decode it...and what it meant.


Mystery signal from a helicopter
http://www.windytan.com/2014/02/mystery-signal-from-helicopter.html

  Last night, YouTube suggested a video for me. It was a raw clip from a
  news helicopter filming a police chase in Kansas City, Missouri. I
  quickly noticed a weird interference in the audio, especially the left
  channel, and thought it must be caused by the chopper's engine. I
  turned up the volume and realized it's not interference at all, but a
  mysterious digital signal! And off we went again.


 -Tom