[amsat-bb] Decoding wideband recordings

Phil Karn karn at philkarn.net
Tue Aug 9 15:54:15 PDT 2011

It's been suggested that I modify my ARISSat-1 BPSK-1000 telemetry
demodulator/decoder to accept wideband quadrature (I & Q) recordings
like those produced by most of the software defined radios out there.

This is fundamentally not that hard, but first I need some information.

How many people could actually use this? What is the format of the
recorded files? Is there a standard, or does each make of SDR produce
its own?

If I could get a good sample wideband quadrature recording of the
ARISSat-1 downlink that includes the BPSK beacon, I could use it for
testing. Ideally there would be no need for any manual tuning because
the wideband recording would always contain the beacon regardless of
Doppler. All tuning would be in the demodulator software.

This might be a little compute-intensive so I can't guarantee that it'll
run in real time on older computers. I already make pretty heavy use of
the Intel SSE (vector arithmetic) instructions for FIR filtering and
Viterbi decoding. The SSE2 set introduced with the Pentium 4 has been
especially useful, so I would consider the P4 (or the AMD equivalent) a
minimum requirement. Of course, the newer and faster the CPU, the
better. I also make use of multiple CPU cores, particularly during the
acquisition phase, so the newer CPUs with lots of CPU cores would also
be preferred.

73, Phil

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