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Comment by jimktrains2 | Hacker News Reader

Perhaps I missed it when I read the article: Why did he originally have the hunch that the radio wouldn't work when Doppler shifted?

Also, I guess something like Manchester encoding wasn't use because of the data rate limitations? IIRC Manchester encoding is self-clocking, which seemed like the issue here.

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He didn't have a hunch, he just knew that the standard comprehensive test was skipped, which is why the standard test procedure only detected a problem, and he had to end early and go off book in order to reveal the doppler problem.

> Fortunately, Claudio Sollazzo, Huygens's ground operations manager at ESA's European Space Operation Centre (ESOC) in Darmstadt, Germany, had a nagging worry about the lack of a full-up communications systems test. Sollazzo knew there was time to run some tests during Cassini's long, uneventful stretches between the planets.

Take this with a grain of salt because it's been a while since I've done telecom/telemetry stuff, but even with a Manchester-encoded signal, one of the first steps in the demodulation process is clock recovery from the signal. This usually involves some sort of PLL (phase-locked loop), which has parameters to control it's freq tracking range. However there are trade offs for widening the range, in terms of time-to-lock and increased probability of locking onto noise etc. so for the original application of the system in earth satellites, they probably used a tight range to improve performance.

Yeah, I'm sure there are good reasons and my armchair analysis is lacking, but by filling in that lacking is a good way to learn:)

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