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Re: [Discuss-gnuradio] Help decoding Bell 202

From: En Shih
Subject: Re: [Discuss-gnuradio] Help decoding Bell 202
Date: Sun, 27 Dec 2015 22:07:46 -0700 (MST)

Thanks, Tim. That really clarified a lot of confusion that I had!

I have uploaded the files here:
-"bell202new.grc" is the current flow graph.
-"dump" is how the input signal I'm trying to decode looks like.
-"decoded" is the bytes of a successfully decoded signal, which was decoded
previously using some hardware equipment. (some parts of the data may be
-"imet.pdf" explains the data packet.
-"tcp.py" explains the data packet.

As far as I know, at the physical layer the data is modulated using Bell
202. The data framing is not AX.25, but conforms to UART, although I'm
unsure about the parity and stop bits. I tried looking for the data frames
by looking for start/stop bits, the header. I've also tried flipping the
bits. However, it still doesn't look quite right.

Correct me if I'm wrong: your FSK demod block uses tone detection to
demodulate, which is passing the signal through two band pass filters in
parallel, and determine which comes through (as in p.9 of

En Shih

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