Radarspotting

hi, not sure where to post this so sorry if it is in the wrong place!

I want to try and decode some messages myself but cant find a spec for the message that contains the Squawk code, after a lot of googling I believe it is in DF5 and possibly DF11 ?

I cant find any document that break these messages down, can anyone point me in the right direction?

I have found this document that decodes DF17 http://www.anteni.net/adsb/Doc/1090-WP30-18-DRAFT_DO-260B-V42.pdf

thanks

Hi,
you can get squawk as below, where *data2, *data3 are pointers to third and fourth byte in DF5 packet data.


unsigned int find_squawk(unsigned char *data2, unsigned char *data3) {
unsigned int squawk = (((*data3 >> 7) & 0x01) << 11) | (((*data2 >> 1) & 0x01) << 10)
| (((*data2 >> 3) & 0x01) << 9) |

(((*data3 >> 1) & 0x01) << 8) | (((*data3 >> 3) & 0x01) << 7)
| (((*data3 >> 5) & 0x01) << 6) |

((*data2 & 0x01) << 5) | (((*data2 >> 2) & 0x01) << 4)
| (((*data2 >> 4) & 0x01) << 3) |

((*data3 & 0x01) << 2) | (((*data3 >> 2) & 0x01) << 1)
| (((*data3 >> 4) & 0x01));

return squawk;
}