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Re: AO40 APOGEE WAV files

Hi Bob,

Many thanks for making these files available. I'll give them a try
with the software demodulator I've been working on. By ear there seems
to be a lot of fast, irregular amplitude fading. I guess that's
because you're looking at the side of the spacecraft and are seeing a
rather irregular sidelobe pattern.

This fading might make it difficult to acquire a whole frame without a
bit error, but I'll try. Even in DSP there's only so much that can be
done with the P3 BPSK format, because it's strongly handicapped by the
lack of any forward error correction.

I know from my own experience in writing a demodulator and decoder for
the ACE spacecraft (which uses concatenated RS/convolutional coding)
that if the signals you recorded had been similarly coded, I'd have no
problem at all in extracting data from them. When testing my ACE
demod, I could solidly recover data from signals that were so weak
that by ear you couldn't even tell they were there.

Many times I've suggested adding FEC to the P3 telemetry downlink
format, but the powers-that-be that designed this stuff in 1975 or so
have never warmed to the idea. Why fix something that's not broken,
they say. Harumph. :-)


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