A first look at TY-2

TY-2 is a 6U Chinese cubesat that was launched on January 19th in a CZ-11 rocket from Jiuquan, together with several other small satellites, including TY-6. According to the IARU Satcoord, TY-2 and TY-6 transmit 9k6 GMSK telemetry in the 70cm Amateur satellite band (435.350MHz for TY-2 and 436.100MHz for TY-6).

Several Amateurs such as K4KDR and PD0OXW have tried to decode the packets from TY-2 and TY-6 without success. I have taken a look to an IQ recording of TY-2 that Scott K4KDR has sent me and at least I've managed to do something (though not much) with it. Here I describe my findings.

The signal is indeed 9k6 FSK. To look at the framing, I've used Michael Ossmann's whole packet clock recovery.

The preamble is formed by a repeating sequence of the bits 1,0. Then the 32bit syncword 0x930B51DE in big-endian notation follows. This is rather interesting, because it is very similar to the behaviour of the NanoCom AX100 (see this post for more information). The AX100 uses the same syncword, but it is transmitted scrambled with a G3RUH scrambler. TY-2 sends the syncword unscrambled. Both the AX100 and TY-2 use the same preamble of repeating 1,0 bits.

I am wondering if TY-2 uses the AX100. I think it would be the first time I see a Chinese satellite using a GOMspace radio (Update: Jan PE0SAT points out that TW-1, -2 and -3 are Chinese satellites using the AX100. I had forgotten this.) Also, I've taken a detailed look at the AX100 manual and it seems that the AX100 can't send the syncword unscrambled. Note that the manual gives the syncword as [0xC9D08A7B] MSB, but this is misleading. This is only correct if each byte is sent starting by the least significant bit, which is not the case for the length field and data.

The syncword 0x930B51DE appears several times inside a single transmission, meaning that there are several contiguous packets in a transmission. Below, we can see the data following the fist syncword. Note that the syncword appears again at positions 0x7b and 0x141.

0000: d7 60 78 7d ea aa c0 71 9d 71 46 8a 2d 93 07 14 
0010: 47 f4 b8 9a 83 3a 6c 83 55 ba c7 6d 41 ee 41 1c 
0020: 39 69 52 3f 21 9b 4a d3 1a 52 09 fa 08 c1 e0 6a 
0030: 76 d9 a0 e1 78 1c 77 47 65 3e 22 a8 2a 0e b5 28 
0040: 2a 18 39 00 e4 ce 8b 6b 54 b1 62 fc 33 40 18 c6 
0050: 70 bf e3 7e bf 76 ff cb 09 14 a7 4f 4f 02 2f a8 
0060: 95 8e 62 8c 72 4b 05 c2 f3 be 1f 65 dd b1 e4 6f 
0070: 65 c1 ac 81 a6 4a 01 79 3b 62 83 93 0b 51 de e6 
0080: f0 c8 7d ea ab c0 71 9d 71 46 8a 2d 93 bb 58 a4 
0090: 90 f0 08 8a a3 fe 01 b5 c5 82 30 88 34 32 69 06 
00a0: 06 b2 3d 81 8e d1 22 14 ef f3 c4 fa bc 73 4e 93 
00b0: 91 54 5e a1 95 50 4d 20 0e 2c 9f e5 e4 e4 80 b4 
00c0: 5e f5 34 77 ad 1b 7b e6 7a 6c e2 68 f6 6d 26 76 
00d0: ca 64 89 10 0d bb bf 04 81 aa 37 23 a1 95 65 ae 
00e0: ad 11 df 58 73 64 5d 76 1b 23 e3 05 6d db 65 47 
00f0: 95 98 3e 0f eb 33 b9 e1 58 9e 3a 95 62 b6 2c 02 
0100: b4 5d 22 28 a6 99 bd 2e 48 79 dc 2e 3a b1 62 fd 
0110: e5 56 65 6f 5e 67 58 d9 0b a8 7c ea ef 5c d0 e7 
0120: e1 c2 e6 22 65 ce 53 8e 32 2b c0 7d 5e 41 96 1a 
0130: 3b 96 f4 bd 90 c6 70 77 b8 6e bb b1 0d 8d 89 3e 
0140: 5d 86 dd 27 17 e2 0f b4 79 79 93 0b 51 de d7 60 
0150: 78 7d ea a8 c0 71 9d 71 a8 8e 2d 93 2e 8c 14 68 
0160: 7c 98 b8 76 08 a3 bc 8a 35 87 6c 35 52 77 05 f6 
0170: e1 29 20 46 b5 a9 d4 e8 6e d4 e0 72 ea 06 4e 11 
0180: a9 4b c9 cf 98 c0 d9 db 7b 73 ac 25 9d 88 fd b2 
0190: 90 47 be 95 45 a4 b6 4d 19 7a ea ba 01 cb 1c 92 
01a0: 26 43 65 f4 ce af b1 c2 d8 1e 99 1f 7f 49 76 94 
01b0: c6 84 25 bf ca 58 a3 b4 7a d9 2f b1 a1 e5 d1 0c 
01c0: ab 51 53 2d 69 aa 45 12 47 18 e4 34 95 69 be 69 
01d0: 24 da 65 2d 5b 

The data seems to be scrambled. I have tried using the G3RUH and CCSDS descramblers, without any luck. I haven't looked at this in great detail, but so far I have the impression that we'll need some information from the satellite team to be able to get any further.

I have added an incomplete decoder for TY-2 to gr-satellites and one sample WAV file to satellite-recordings. I would be glad if anyone can provide some additional information regarding the TY satellites.

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