Need help decoding of FLARM (868.2/868.4MHz)

Nick Foster bistromath at gmail.com
Fri Dec 6 17:33:39 UTC 2013


OK, turns out someone beat us to it a while ago, even going so far as to
reverse-engineer the cheesy crypto FLARM put in there to discourage
copycats. The PHY is a Nordic nRF905 (+10dBm output), the medium access
control is blind random-interval squitter with no two-way communication,
and all Onera's vaunted "prediction" logic is being done in an AVR (!).
Kids these days...

http://pastebin.com/8ke6jnQZ

The good news is Manchester-encoded GFSK is dead simple to decode, and the
known parameters of the nRF905 make it easy to write a receiver.

--n


On Fri, Dec 6, 2013 at 8:14 AM, Nick Foster <bistromath at gmail.com> wrote:

> This is a new one! Thanks for bringing it to my attention. Looks like a
> voluntary, GPS-based (i.e., not secondary surveillance) system. While the
> serial protocol appears to be NMEA-like, the protocol "under the hood" at
> the PHY layer could be basically anything, and the FLARM consortium appears
> to have elected to keep specs hidden. Reading the dataport specification
> gives few insights as to the PHY layer, but at least it's good to know the
> protocol has "future-proof" support for all aircraft types.
>
> [image: Inline image 1]
>
> If you record good FLARM transmissions I am happy to assist in decoding
> what I can, not least because proprietary protocols were meant to be open.
> =)
>
> --n
>
>
> On Fri, Dec 6, 2013 at 7:58 AM, Fritz Meier <fritz.meier at myway.de> wrote:
>
>> Hi, to all
>> after I've seen with RTL ADSB and DUMP1090 how ADS-B transponder data
>> 1090MHz (pulse modulation) is decoded I would like to start with FLARM
>> (Europe 868.2 and 868.4MHz frequency modulated). The position data of
>> gliders
>> (ID, latitude, longitude and altitude) are sent 1xsec in the form of
>> NMEA-like records.
>> I work with the BeagleBone black and have a FLARM transmitter installed
>> near
>> the RTL-Dongle/Antenne and may at any time start recording I/Qsamples
>> with RTL_SDR.
>> Thanks
>> Fritz
>>
>>
>
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