Well, I hope Airnav don't mind me posting this - I hope it simply illustrates the futility of attempting this.
I have tried reading data direct from the radar box, and this is what I learnt. All you will see is a phase modulated signal in its raw form. Some charting of the signal shows that you would also need to shift bit values to align on word boundaries, and the amount you need to shift fluctuates over time.
So, taking this packet as an example:
11 60 7f 80 7f 87 87 80 7f 00 7f 80 78 78 70 78
78 78 38 78 78 7f 80 7f 00 7f 00 78 7f 87 80 78
7f 80 7f 07 87 c7 80 7f 80 78 7c 70 78 7f 80 7f
00 7c 78 7f 87 c7 87 83 00 78 00 0a
With a phase shift of -3, gives this waveform:
This looks like a phase modulated, 56-bit short squitter with preamble - A DF11 for 400A99.
Good luck developing software to process the raw data.