Signal was really strong, SNR was high, but I was kind of concerned by the waterfall. There was a ribbed or chain-mail texture to the modulation, like they were individual subcarriers being overmodulated or modulated with the wrong constellation (QPSK), and that was something I had never seen before. There were also serious decoding issues, with silent audio frames, a snippet of audio, and then a series of undecodable frames.
When the transmission abruptly stopped around 20:01 UTC I thought they might fix it. No such luck.
I tried widening the bandwidth and re-centering, thinking that may have actually helped. But with an SNR of 25 dB, frequency tracking was obviously not the issue.
As you can see from the above, solid audio decoding began around 20:45 UTC, the last 15 minutes of the broadcast. This was marked by a disappearance of that ribbed texture. But it made one final appearance, and audio dropped out in response.
One thing that I should have done was check the MSC constellation to see if it was indeed not using all elements of the 64-QAM alphabet.
Redeeming quality: Stable frequency offset (about 5 Hz if I recall correctly).
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