[HH] Mystery signal from a helicopter

[Tom Metro]

Jerry Feldman wrote:
> 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
>
> ...helicopters have 2 different vibration levels, low freq and high
> freq. ... The low freq is caused by the main rotor blades. ... The
> tail rotor is the cause of the high freq.

Interesting, but did you read the article? It wasn't about an analog
sound resulting from a vibration, but instead a digital signal imposed
on the left audio channel, that when decoded turned out to contain the
GPS coordinates of the helicopter.

 -Tom