how to decode ads-b raw data

[yutingtai]

Hi everyone,

I want to decode the ads-b data from a UDP multicast server. The server only provides binary raw data, so I’m quite confused about how to use pms.tell(msg) with the correct input from the raw data when I receive it. I know the ads-b message consists of 112 bits or 28 long hexadecimal format or it has a shorter message version, and mode-s message comes with a specific preamble.
My current thought is to parse the data I receive. I used hexdump to get the below data from the UDP multicast server and tried to require the decode information from pms.tell(“3015f5cf3919c34340632a204001”) but the result doesn’t seem correct. Should I check the preamble and then decode it? or how should I actually decode it?

I have been reading pyModeS/pyModeS/streamer/modeslive.py and decode.py to try to understand how pymodes decode the ads-b from raw data, but still feel not clear about it.

Hope to hear from anyone soon! Thank you and Happy New Year.

[yutingtai]

Hi everyone,

I have some new understanding about my previous question, so what my message seems wrong was because I received the raw data and converted it with the hexdump immediately. However, I might not receive the complete message at first, so using hexdump would cause the problem I asked above (pms.tell(“3015f5cf3919c34340632a204001”) doesn’t seem correct), right?

I now converted the raw bytes into binary format, and tried to retrieve the message. I searched “10001” (DF: 17) in the output file and got some “seem-correct-messages” , one of them was like: 8D7C857E94748B737F8182798267. But how can I be sure this is the correct message to decode?

I used another c library: dump1090 to decode the same file, but the output didn’t contain the message I found in the previous step. Is my understanding correct in the previous step?? or what should I actually do to get the correct message to decode it.

Thanks again !