Opensky

[SCPD]

Here's a screenshot of a live OpenSky signal in Austin Texas on 935.7 Mhz as viewed through UniScope. There's a remarkably clear eye pattern. Apparently OpenSky is C4FM at 4800 baud (much like non-simulcast P25). That's 9600 bits per second.

[ insert evil mad scientist laughter here ]

Seriously though - this is puzzling because I thought OpenSky was based on CDPD technology which hums along at 19200 bits per second. Perhaps they scaled back the baud rate to fit inside a 25 khz channel. Recall that the old analog cellular networks were 30 khz wide.

Interesting ...

 

[SCPD]

Here's the data sliced as if it were two level data (discarding half the bits). I'm just looking for a frame sync pattern at this point. It looks to be highly repetitive 35 byte messages (70 actual bytes).

E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 0C 2A AE F8 95 25 F8 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 0D DD 39 76 21 F8 80 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 04 6E 91 5E 18 25 78 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 CF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 05 99 06 D0 AC F8 00 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 08 BA 97 78 D2 83 68 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 63 51 A3 03 ED 5C 49 4E 2A 09 4D 00 F6 66 5E 10 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 00 FE A8 DE 5F 83 E8 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 CF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 01 09 3F 50 EB 5E 90 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 09 22 51 0B 01 ED E0 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 63 51 A3 03 ED 5C 49 4E 2A 08 D5 C6 85 B5 30 98 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 01 66 6E AD 8C ED 60 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 00 91 F9 23 38 30 18 49 1D 8E B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 0C 46 FF 05 F2 96 68 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 05 F5 57 2D CB 4B 90 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 04 02 C0 A3 7F 96 E8 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 0C 29 AE F8 95 25 98 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 0D DE 39 76 21 F8 E0 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 04 6D 91 5E 18 25 18 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 05 9A 06 D0 AC F8 60 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 CF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 08 B9 97 78 D2 83 08 49 0D 86 B4 60 F3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 09 4E 00 F6 66 5E 70 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 CF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 00 FD A8 DE 5F 83 88 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 01 0A 3F 50 EB 5E F0 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 73 51 A3 03 ED 5C 49 4E 2A 09 21 53 1B 01 ED 80 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 73 51 23 03 ED 5C 59 4E 2A 08 D6 C6 85 B5 30 F8 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 62 51 A3 03 ED 5C 49 4E 2A 01 65 6E AD 8C ED 00 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 00 92 F9 23 38 30 78 69 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 62 51 A3 03 ED 5C 49 4E 2A 0C 45 FF 05 F2 96 08 49 0D 86 B4 60 F3 2D 6B BE 33 37 2C B8
E1 94 EF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 05 F6 57 2D CB 4B F0 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0
E1 94 EF 8B D7 71 62 51 A3 03 ED 5C 49 4E 2A 04 01 C0 A3 7F 96 88 49 0D 86 B4 60 B3 2D 6B BE 33 37 2C B8
E1 94 CF 89 D7 71 62 51 23 03 ED 5C 59 4E 2A 0C 2A AE F8 95 25 F8 49 0D 86 B6 60 B3 2D 6B BE 33 37 2C A0

Here's more of the same ...

2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 05 99 06 D0 AC F8 01 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 08 BA 97 78 D2 83 69 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 09 4D 00 F6 66 5E 11 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 00 FE A8 DE 5F 83 E9 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 01 09 3F 50 EB 5E 91 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 09 22 51 1B 01 ED E1 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 08 D5 C6 85 B5 30 99 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 01 66 6E AD 8C ED 61 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 00 91 F9 23 38 30 19 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 0C 46 FF 05 F2 96 69 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 05 F5 57 2D CB 4B 91 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 04 02 C0 A3 7F 96 E9 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 0C 29 AE F8 95 25 99 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 0D DE 39 76 21 F8 E1 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 04 6D 91 5E 18 25 19 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 05 9A 06 D0 AC F8 61 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E6 42 40 63 EF CF 21 90 49 4E 2A 08 B9 97 78 D2 83 09 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 09 4E 00 F6 66 5E 71 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E4 42 40 63 EF CF 21 90 49 4E 2A 00 FD A8 DE 5F 83 89 D0 94 1F 25 53 9F 5F 0B D8 59 58 5B 78
2D 58 23 40 E6 42 40 63 6F CF 21 90 59 4E 2A 01 0A 3F 50 EB 5E F1 D0 94 1F 27 53 9F 5F 0B D8 59 58 5B 60
2D 58 23 42 E6 42 40 63 EF CF 21 90 49 4E 2A 09 21 53 1B 01 F9 81 D1 B4 1F 25 53 9F 5F 0B D8 59 58 5B 78

 

[SCPD]

... and here's my best guess for a 24 bit frame synchronization pattern.

94E2A0 or 100101001110001010100000

It's the only run of consecutive bits that is consistent in the two blocks posted above.

Extending the above assumption, 512 bits of unprotected data follow. At 560 bits total - including the sync bits - that's 120 packets every 7 seconds.

 

[inigo88]

It's alive, it's alive!!! Muhahaha!!!

Great work!

 

[SCPD]

Here's a hex dump of the raw data - minus what I believe to be the frame synchronization bits.

Each line of text is one 64 byte message.

 

[SCPD]

The next release will dump Opensky packets to the decode log. Sorry, no annotation - just hex bytes.