[HH] Mystery signal from a helicopter

[Jerry Feldman]

On 02/02/2014 07:30 PM, Tom Metro wrote:
> 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.
>
I did read that, and the aviation radios were probably specialized to
filter out and vibration effects. It is interesting that the modem was a
Bell 202 ASCII, but previously he said it was a Nucomm Skymaster TX,
which was built for aircraft use.

-- 
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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