[HH] Mystery signal from a helicopter

[Jerry Feldman]

Most helicopters used by news organizations are turboshaft. Only the
smallest helicopters these days use piston engines. The turboshaft would
emit a constant. But.... helicopters have 2 different vibration levels,
low freq and high freq. These vibrations are why a helicopter's main
mission in life is self destruction.  The low freq is caused by the main
rotor blades. Depending on whether they are semi-rigit or fully
articulated, each blade has its own independent angle of attack,. and
angle between the blades an plane of rotation. The tail rotor is the
cause of the high freq. I have seen helicopters go into vibration on the
ground and destroy themselves.

On 02/02/2014 02:11 AM, Tom Metro wrote:
> 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
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>

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
PGP key id:3BC1EB90 
PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66  C0AF 7CEA 30FC 3BC1 EB90


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