[FPSPACE] EVA....Both crew are out !!!

[gorski]

I didn't see the video yet, John (just waking up where I am, and yesterday
was a long day)--but the digital/analogue remark is true--sort of.   I
used to work on video streaming hardware, so I'll throw in my
only-tangentially-relevant two cents here.

There are one of two things I think are likely to have caused the hiccup
you describe in the video--either technical problems switching the feed
from one source to another, or good old-fashioned signal degradation.

If it was just that they were way at the edge of one station's range, the
image degradation would likely have started a while before--one of the
advantages of digital is if you can recover the signal well enough to get
anything out of it, you may well get everything out of it--a weakly
detectable transition still gives you your 1 or 0.  Digital dropout would
usually only happen where the analog picture's pretty terrible--there,
maybe, though barely.

And if it was a problem handing off the digital source from one base
station to the other--well, the technology exists--you do that with your
cellphone all the time!  It just takes some extra work.  (You do still
have to hand off sources with an analogue receiver too, though...)

So analogue might have its advantages in that the signal's a little
tougher to kill completely, but for most of the time you're getting a
crystal-clear picture instead of one plagued by static and ghosts.


Good morning, and let me just add my congratulations to the crew of
Shenzhou VII.

--me



On Sat, 27 Sep 2008, John Locker wrote:

}Both crew members have emerged from the airlock...one waving a chinese flag
}
}Interestingly there was a picture break up as the signal was passed from one
}tracking station to another....There was an instant loss of image as they
}are using full digital downlink , where as , had this been analogue , we
}would have seen a gradual degradation of image .....This illustrates one of
}the major drawbacks of digital versus analogue.
}
}John
}
}
}
}http://satcom.website.orange.co.uk/
}
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