Observation 384186: CHOMPTT (43855)

Satellites & Observations Observations
1

Regarding Observation 384186 …

direwolf decodes one packet in this observation:

WI2XVT audio level = 1(1/1)   [NONE]   ___|_____
[0.3] WI2XVT>WI2XVT,WI2XVT:CHOMPTT<~!'k`/-!UMk;9o@<""4-N!3$&#!)s#)!aPk?!b_X(!lG,Y!#5M,"&K!("&]+b!29Gn!!!"t!!*))!?V:A?pd?_^f*Z%JD*B~>
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U frame UI: p/f=0, No layer 3 protocol implemented., length = 128
 dest    WI2XVT  0 c/r=0 res=3 last=0
 source  WI2XVT  0 c/r=0 res=3 last=0
 digi 1  WI2XVT  0   h=0 res=3 last=1
  000:  ae 92 64 b0 ac a8 60 ae 92 64 b0 ac a8 60 ae 92  ..d...`..d...`..
  010:  64 b0 ac a8 61 03 f0 43 48 4f 4d 50 54 54 3c 7e  d...a..CHOMPTT<~
  020:  21 27 6b 60 2f 2d 21 55 4d 6b 3b 39 6f 40 3c 22  !'k`/-!UMk;9o@<"
  030:  22 34 2d 4e 21 33 24 26 23 21 29 73 23 29 21 61  "4-N!3$&#!)s#)!a
  040:  50 6b 3f 21 62 5f 58 28 21 6c 47 2c 59 21 23 35  Pk?!b_X(!lG,Y!#5
  050:  4d 2c 22 26 4b 21 28 22 26 5d 2b 62 21 32 39 47  M,"&K!("&]+b!29G
  060:  6e 21 21 21 22 74 21 21 2a 29 29 21 3f 56 3a 41  n!!!"t!!*))!?V:A
  070:  3f 70 64 3f 5f 5e 66 2a 5a 25 4a 44 2a 42 7e 3e  ?pd?_^f*Z%JD*B~>
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1 Like
2

Replaying IQ data for this CHOMPTT observation through gqrx using the AFSK1200 decoder yields these packets:

14:34:01$ fm WI2XVT-0 to WI2XVT-0 via WI2XVT-0 UI PID=F0
CHOMPTT<~0im^!.U3&F$(1ld!'+&!<$,!)Gn!T50!bML!!mUm-!"K#+"!R_O"&T%5!20Am!!*)4!!!"p!?D.?G_/?aclbaWJ5Sc~> 14:34:02$ fm WI2XVT-0 to WI2XVT-0 via WI2XVT-0 UI PID=F0 OPTI<~\HF"+-%amF9*3UofF&RI!!!!!!!!!!AUAnk+TM~> 14:35:01$ fm WI2XVT-0 to WI2XVT-0 via WI2XVT-0 UI PID=F0 CHOMPTT<~10,k^.U3%_$(M)g!*'+&!<*$,!)3Mn!K/!al’m!o3r1!!‘0!“f4D”&],’!1s5k!!)G!!!Q!?hFC(l^ra^t;$T!;jY~>
14:35:02$ fm WI2XVT-0 to WI2XVT-0 via WI2XVT-0 UI PID=F0
OPTI<~\HF"±%amF93UofF&RI!!!AUAnk+TM~>
14:36:01$ fm WI2XVT-0 to WI2XVT-0 via WI2XVT-0 UI PID=F0
CHOMPTT<~1KJF.U3%#$-!'<!'+&!<$,!)3Mo!`];/!aYpj!qHF;!:p:D!!E;"&T&J!1a)i!!!#S!!!"W!?hFCn6\Ta5WhI8i4[&~>
14:36:02$ fm WI2XVT-0 to WI2XVT-0 via WI2XVT-0 UI PID=F0
OPTI<~\HF"±%amF9*3UofF&RI!!!AUAnk+TM~>

I wasn’t aware that the gr-satnogs AFSK1200 decoder only decodes AX.25 frames. How hard would it be to adapt it for regular frames?

3

Not sure what you’re asking for: the frames you show seem to be AX.25 frames…

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4

I’m confused. Why does the gr-satnogs afsk1200_ax25 decoder not decode these?

5

The CHOMPTT is an APRS sat. APRS uses standard AX.25 headers with an awful APRS compressed digital data stream, which is what we see in the decoded post above. So, gr-satnogs AFSK1200 should decode the headers in plain english. The data will still be compressed. Possiblilty that the gr-satnogs decoder is shifting a bit somewhere and the header is not timed correctly.