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Re: Observed AO-40 FEC coded telemetry



Kazu Sakamoto writes:
>On Saturday June 7th 2003 around 03z, I am sure
>that I observed the experimental transmission of
>FEC coded telemetry of AO-40 on the S2 beacon.
[some text deleted]
> Unfortunately since I'm not ready to decode
>the FEC coded blocks, I coundn't confirm what
>contained in the 13 seconds.

It looks like a FEC block after the normal telemetry
block, I think.

I downloaded the WAV files from
http://www.ne.jp/asahi/hamradio/jj1wtk/
and tried to process them using Phil Karn's AO-40
FEC code.  To do this I first converted a small
portion of the WAV file from 16bit 8000 samples per
second to 16bit 9600 samples per second, which is
the format that Phil's programs use.

Running dpsk_demod on the converted portion of the
WAV file shows that the Phil's code is able to
correctly detect the carrier just below 1600 Hertz,
and the sync is mostly zeros with a few -1's which I
think means that the symbol sync is working fine.
I take this to mean that the dpsk_demod is seeing
the bits and bit transitions okay.

However, the program doesn't get out of search mode.
The Viterbi decoder histogram shows that most of the
bits are being decoded as nearly halfway between
"strong one" and "strong zero".  For most frames the
biggest number is near the center of the list.
The Reed Solomon decoder says "FAIL FAIL" indicating
that it sees too many errors to correct.

Probably I'm doing something wrong here.  Has anyone
gotten a FEC block to demodulate ?

Douglas KA2UPW
"I'm working on putting the code into AO40Rcv...want to help?"
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